
Book . 574 

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WORKS OF 

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PUBLISHED BY 

JOHN WILEY & SONS 



A Text=Book on Roads and Pavements. 

The aim of this work is to give a brief dis- 
cussion, from an engineering standpoint, of the 
principles involved in highway work, and to 
outline the more important systems of construc- 
tion, with a view to forming a text which may 
serve as a basis for a systematic study of the 
subject. i2mo, cloth, $2.00. 

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This work embodies the results of a careful 
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i2mo, cloth, $2.00. 



A TEXT-BOOK 



ON 



Roads and Pavements. 



BY 



FREDERICK P. SPALDING, 

Assistant Professor of Civil Engineering in Cornell UniMersity^ 
■ Member American Society of Civil Engineers, 



SECOND EDITION, REVISED AND ENLARGED. 
FIRST THOUSAND. 



> • 



1 •> ) 



? ^ i , ' J > i o ? > 



• o 



- ' » 



NEW YORK: 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1902. 



THF I.II8RARY OF 

GONG??ES8, 
Two OofffM Heoejved 

JAN. 27 1902 

CercSIOMT ENTRY 

EkjLASS » XXa NO. 
COPY a 



Copyright, 1894, 1902. 

BY 

Fredbrick p. Spalding. 



,00 e«« 
- c t « 



BOBBRT DRUMMOND, ELECTROTVPKR AND PRINTER, NEW YORK. 




PREFACE. 



Successful practice in the construction of highways 
must depend upon correct reasoning from elementary 
principles in each instance rather than upon following 
definite rules or methods of construction. 

The aim of this book is to give a brief discussion, 
from an engineering standpoint, of the principles in- 
volved in highway work, and to outHne the more im- 
portant systems of construction, with a view to form- 
ing a text which may serve as a basis for a systematic 
study of the subject. 

Details and statistics of particular examples have 
for the most part been excluded as undesirable in a 
book of this character. Such information is available 
in many forms for those having the necessary ele- 
mentary training and experience to enable them to 
properly use it. 

Considerable space has been given to the location 
and construction of country roads, as seemed proper 
in view of the present general public interest in the 
matter, and the probable development of this new field 
of activity in engineering work. The improvement of 
our common roads must come through transferring 
such work to the charge of those who make it a profes- 
sion, and not through teaching the public how roads 
should be constructed. 

F. P. S. 
Ithaca, N. Y., July, 1894. 



NOTE TO SECOND EDITION. 



In the present edition, in addition to numerous 
small changes and corrections, the chapter on Brick 
Pavements and the article on Street Railway Track 
have been entirely rewritten, an effort being made 
to briefly represent the best recent practice in such 
work. 

F. P. S. 

Columbia, Mo., November, 1901. 



IV 



CONTENTS. 



CHAPTER I. 

GENERAL CONSIDERATIONS. 

PAGE 

Art. I. Object of Roads i 

2 . Resistance to Traction 2 

3. Tractive Power of Horses 7 

4. Desirability of Various Surfaces 9 

5. Economic Value 11 

6. Healthfulness 14 

7. Safety 16 

8. Durability 18 

CHAPTER n. 

DRAINAGE OF STREETS AND ROADS. 

Art. 9. Necessity for Drainage 22 

10. Surface Drainage 23 

11. Subsurface Drainage 26 

12. Kinds of Soil 28 

13. Types of Drains 31 

14. Culverts 34 

1 5. Water-breaks 42 

CHAPTER HI. 

LOCATION OF COUNTRY ROADS. 

Art. 16. Considerations governing Location 43 

17. Length of Road 47 

V 



vi CONTENTS. 

PAGE 

Art. i8. Rise and Fall 49 

19. Rate of Grade 51 

20. Examination of Country 53 

21. Placing the Line 56 

22. Comparison of Routes 59 

23. Changing Existing Locations 63 

CHAPTER IV. 

IMPx^OVEMENT OF COUNTRY ROADS. 

Art. 24. Nature of Improvements 6y 

25. Earthwork 68 

26. Drainage 72 

27. Earth-road Surface 73 

28. Gravel Roads 76 

29. Maintenance of Country Roads 78 

30. Width of Country Roads. 80 

31. Economic Value of Road Improvements 82 

32. Systems of Road Management 85 

CHAPTER V. 

BROKEN-STONE ROADS. 

Art. 33. Definition 88 

34. Macadam Roads 89 

35. Telford Foundations 91 

36. Choice of Foundation 93 

37. Materials 96 

38. Binding Material loi 

39. Compacting 103 

40. Thickness of Road Covering 105 

41. Cross-section 107 

42. Maintenance 107 

CHAPTER VL 

FOUNDATIONS FOR .PAVEMENTS. 

Art. 43. Preparation of Road-bed 1 10 

44. Purpose of Foundation m 



CONTENTS. Vli 

PAGE 

Art. 45. Sand Foundation 112 

46. Gravel and Broken Stone 113 

47. Concrete 114 

48. Brick 116 

49. Sand and Plank 117 

50. Depth of Foundation 117 

CHAPTER VII. 

BRICK PAVEMENTS. 

Art. 51. Paving Brick 119 

52. Tests for Paving Brick 126 

53. Foundations 140 

54. Construction 141 

55. Maintenance 149 

CHAPTER VIII. 

ASPHALT PAVEMENTS. 

Art. 56. Asphaltum 151 

57. Rock Asphalt 157 

58. Asphalt Blocks 160 

59. Foundations 162 

60. Construction 164 

61. Vulcanite or Distillate Pavement 166 

62. Maintenance 167 

CHAPTER IX. 

WOOD PAVEMENTS. 

Art. 63. Wood Blocks 169 

64. Foundations 172 

65. Construction 174 

66. Preservation of Wood 1 79 

67. Maintenance 182 

68. Healthfulness 183 



Vlll CONTENTS. 

CHAPTER X. 

STONE-BLOCK PAVEMENTS. 

PAGE 

Art. 69. Stone for Pavements 186 

70. Cobblestone Pavements 188 

71. Belgian Blocks 190 

72. Granite and Sandstone Blocks 190 

73. Construction < 191 

74. Stone Trackways 194 

CHAPTER XL 

CITY STREETS. 

Art. 75. Arrangement of City Streets 196 

76. Width and Cross-section 2or 

'j'j. Street Grades 205 

78. Street Intersections 207 

79. Footways 209 

80. Curbs and Gutters 214 

81. Crossings 220 

82. Street-railway Track 221 

83. Trees for Streets 233 

84. Alleys 235 



A TEXT-BOOK 



ON 



ROADS AND PAVEMENTS. 



CHAPTER I. 
GENERAL CONSIDERATIONS. 

Art. I. Object of Roads. 

The primary object of a road or street is to provide 
a way for travel, and for the transportation of goods 
from one place to another. The facility with which 
traffic may be conducted over any given road depends 
upon the resistance offered to the passing of vehicles 
by the surface or the grades of the road, as well as 
upon the freedom of movement allowed by the width 
and form of the roadway. In order that a road may 
offer the least resistance to traffic, it should have as 
hard and smooth a surface as possible, while affording 
a good foothold to horses, and should be so located as 
to give the most direct route with the least gradients. . 

The expediency of any proposed road construction 
or improvement depends upon its desirability as affect- 
ing the comfort, convenience, and health of residents of 



2 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the locality, and also upon its economic value which is 
largely determined by its cost and durability, as well 
as upon the facility it gives for the conduct of traffic. 

The problem of the highway engineer, in designing 
works of this character, involves the consideration of 
these various elements and their proper adjustment to 
give the best results. 

. The kinds of road surface most commonly employed 
are as follows : For the streets of cities and towns, 
pavements of stone blocks, brick, asphalt, and wood ; 
for suburban streets and important country roads, 
macadam and gravel surfaces ; for ordinary country 
roads in general, surfaces of earth or gravel. 

Art. 2. Resistance to Traction. 

The resistance to traction of a vehicle on a road 
surface may be divided into three parts : axle friction, 
rolling resistance, and grade resistance. 

Axle /rzcHon varies with, the nature of the bearing 
surfaces, and for vehicles of similar construction is di- 
rectly proportional to the load. It is entirely inde- 
pendent of the nature of the road surface. 

Rolling resistance is of two kinds : that due to irregu- 
larities in the surface of the road, and that of a wheel 
to rolling upon a smooth surface, sometimes called 
rolling friction. 

The resistance due to an inequality in the road sur- 
face, is the horizontal force necessary, at the axle, to 
raise the weight upon the wheel to the height of the 
obstacle to be passed. Thus (Fig. i), by the principle 

of the lever, P=W~. 

a 



GENERAL CONSIDERATIONS. 3 

For small inequalities, this resistance will be approxi- 
mately inversely as the diameter 
of the wheel. The effect of small y'^ ^\ 
irregularities in the surface, how- /^ \ 

ever, is due more to the shocks and / I \ 

concussions produced by them than pl H" I / 

to the direct lifting: action of the \ ^ :' / 

obstacle, and the resistance due to t^f::P-\ ^^ 

uneven surface is greater at high p 

than at low velocities. 

Rolling friction is probably due for the most part to 
the compressibility of the surface of the road, which 
permits the wheel to indent it to some extent. The 
wheel is thus always forcing a wave of the surface 
before it, or climbing an inclination caused by its 
weight upon the road surface. This rolling friction 
varies for wheels of differing diameters, being less for 
large than for small wheels. The experiments of M. 
Morin, in France, seemed to indicate that the resist- 
ance varies inversely as the diameter. Other experi- 
ments have indicated a less variation, approximately 
as the square root of the diameter, while Mr. D. K. 
Clark (Roads and Streets by Law and Clark ; London, 
1890) concludes, from a mathematical discussion based 
upon the assumption that the material of the surface 
is homogeneous and the pressure proportional to the 
depth of penetration, that the resistance to traction 
is inversely as the cube root of the diameter of the 
wheel. 

For practical purposes it may be considered that, for 
wheels of ordinary sizes used on road vehicles, the 
rolling resistances are equal to the load multiplied by a 
coefficient which depends upon the nature and condi- 



4 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

tion of the road surface, although these coefficients 
are somewhat affected by the sizes of the wheels. 

Many experiments have been made for the purpose 
of determining the tractive force required for a given 
load upon various road surfaces. The results show 
somewhat wide variations, as would be expected when 
the many elements that may affect them are con- 
sidered. The following table shows a few average 
results, which will give some idea of the relative resist- 
ances of various surfaces and of the advantage to be 
derived from a smooth and well-kept road surface : 

TRACTIVE RESISTANCES ON VARIOUS SURFACES. 

Character of Road. Resistance, Lbs. per ton. 

Earth — ordinary in fair condition. 125 to 140 

dry and hard 60 " 100 

Macadam — very good 40 . " 60 

ordinary 60 " 80 

poor., 100 '' 150 

Granite-block pavement — good. . . 25 * 4.Q 

ordinary 50 '* 80 

Asphalt pavement 15 " 25 

Wooden-block pavement 20 " 30 

On earth roads or smooth pavements the tractive 
force is independent of the velocity ; but on rough 
pavements, where concussions take place, the tractive 
force increases as the speed increases. 

Grade Resistances. — Tractive resistance due to grade 
is independent of the nature of the road surface, or of 
the size of the wheels. It is equal to the load multi- 
plied by the sine of the angle made by the grade with 



GENERAL CONSIDERATIONS. 



5 



the horizontal. Thus in Fig. 2 the tractive force P, 
due to the grade, is the force necessary to prevent the 
wheel from rolling down 
the slope under the ac- 
tion of the weight W^ or 
it is the component of 
^parallel to the slope ac. 



ac 




Fig. 2. 



Grades are ordinarily expressed in terms of rise or 
fall in feet per hundred, or as percentage of horizontal 
distance. 

For all ordinary cases of small inclinations ab is 
approximately equal to ac, and we may take 

be 

or the tractive force necessary to overcome any grade 
equals the load multiplied by the percentage of 
grade. 

The total tractive force necessary to haul a load up 
an inclined road equals the sum of the force necessary 
to haul the load upon the same surface when level, and 
the force necessary to overcome the grade resistance. 
Thus, if we wish to find the tractive effort necessary to 
haul a load of 2 tons up a grade of 3 ft. in 100 over a 
good macadam road. Taking the resistance of the 
road surface when level at 60 lbs. per ton, we have for 
the total resistance 



R^2y.fy^-\- 4000 X TTJT = 240 lbs. 



6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In going down the grade, the force due to grade 
becomes a propelHng force, and the tractive effort 
required is the difference between the surface resist- 
ance and grade force. In case the grade force be the 
greater, the resulting tractive force becomes negative, 
or it will be necessary to apply the force as a resistance 
to prevent acceleration of the velocity in the descent. 

The angle for which the tractive force required for a 
given surface equals the grade resistance is called the 
Angle of Repose for that surface. In the case given 
above, 2 X 60 — 4000 X yf 0^ = o, or the angle of repose 
for a surface whose level resistance is 60 lbs. per ton is 
.a 3^ grade. If a vehicle were left standing upon that 
inclination, it should remain standing with the forces 
just balanced. If it were started down the grade, it 
should continue to move at a uniform rate, without 
the application of any other force. 

In a series of experiments made by the Studebaker 
Brothers Manufacturing Company (see The Engi- 
neering Record for Dec. 16, 1893) upon the traction 
necessary upon various surfaces with American wagons, 
it was found that the width of wheel-tire has little if 
any effect upon a hard surface ; that there was a small 
difference in favor of the wide tire upon soft ground, 
and upon sod the narrow tire would cut through where 
the wide one would pass over. 

The wheels used in the tests had tires if, 3, and 
4 inches wide, and varied from 3 ft. 6 in. to 4 ft. 6 in. 
in diameter. 

The general results show a variation in tractive force 
required, depending upon the construction of the 
vehicle, of from 30 to 65 pounds per ton for a stone- 
block pavement, from 120 to 175 pounds per ton for a 



GENERAL CONSIDERATIONS. 7 

good sand road, from 60 to 100 pounds per ton for a 
gravel road, and from 240 to 325 pounds per ton on a 
muddy road. 

It was also found that the force necessary to start 
the load was from 125 to 200 pounds per ton greater 
than that necessary to keep it in motion ; the load 
starting easier on wheels of large diameter than upon 
small ones, but the diameter seemingly having less 
effect upon the traction when in motion. 



Art. 3. Tractive Power of Horses. 

The loads that a horse can pull upon various road 
surfaces will not necessarily be proportional to the 
resistance offered by the surface to traction, as the 
tractive force that the horse can exert depends upon 
the foothold afforded by the surface. The ability of a 
horse to exert a tractive force depends upon the 
strength of the animal, upon his training for the par- 
ticular work, and whether he be accustomed to the 
surface upon which he is travelling. The work of dif- 
ferent animals is therefore subject to considerable varia- 
tions, and only very rough approximations are possible 
in giving average values of the work a horse may do 
under differing conditions. 

The tractive force that may be exerted by a horse, 
at moderate speeds, varies approximately inversely as 
the rate of speed ; or, in other words, the power that a 
horse can exert through any considerable time is nearly 
constant for varying velocities. Thus it may be as- 
sumed, as an average value, that a horse working 
regularly ten hours per day can put forth a tractive 



8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

effort of 80 pounds at a speed of 250 feet per minute 
on an ordinary level road surface. 

For the power of the horse we then have 

Power = force X velocity = 80 X 250 = 20000 foot-lbs. 

per minute. 

For any other rate of speed, as 200 feet per minute, 
we would have 20000 -=- 200 =100 pounds as the 
tractive force exerted by the horse. 

If the period of daily work be lessened, the power 
that may be developed will be increased, either by in- 
creasing the load or the velocity. 

The tractive force that a horse is able to exert de- 
creases very rapidly as the rate of inclination increases. 
This is due both to the expenditure of power by the 
horse in lifting his own weight up the grade, and to 
the less firm footing on the inclination. The effect of 
differences in the foothold afforded by various pave- 
ments is very marked in the loss of tractive power 
upon grades. 

In the table below are given the loads that an 
average horse may be expected to continuously haul 
up different inclinations, on various road surfaces, at 
slow speed. These figures, while of little value as an 
absolute measure of what may be done in any par- 
ticular case, are of use as a rough comparison of the 
relative tractive properties of different surfaces and 
grades. The effect of grades upon tractive effort will 
also depend upon the condition in which the surface is 
maintained, and upon the weather. Snow and ice in 
winter, or the damp and muddy condition of some 
pavements in wet weather, have a very considerable 
effect to diminish tractive power. 



GENERAL CONSIDERATIONS. 



LOADS IN POUNDS THAT A HORSE CAN DRAW UPON 
VARIOUS SURFACES AND GRADES. 



Kinds of Surface. 


Rate of Grade. 


Level. 


I in 
100. 


2 in 
100. 


sin 
100. 


4 in 
100. 


sin 
100. 


10 in 
100. 


15 in 
100. 


Earth road — g^ood 


3000 
1300 
4000 
1600 
6000 
3000 

lOOOO 


2400 

IIOO 

2700 

IIOO 

4500 

2300 
4000 


2000 
900 
2000 
800 
3300 
1700 
2500 


1600 
700 
1600 
600 
2700 
1400 
1800 


1400 
600 

1400 
500 

2200 

IIOO 

1300 


1200 

500 

1200 

450 
1700 

900 
1000 


800 
400 
700 
250 
900 

450 
400 


300 

150 
200 
100 
400 
200 


poor 


Broken-stone — good 

poor 

Stone Blocks — good 

poor 

Asphalt — clean and dry 



On steep grades (more than 8 or 10 in 100) special 
forms of block pavements are sometimes employed to 
increase the tractive power by affording better foot- 
hold to horses. Sheet asphalt is not usually employed 
on grades of more than 4%. Ordinary wood blocks 
and brick are used up to grades of 7^ or S%, and granite 
blocks to 10^. 

A horse may frequently exert for a short time a 
tractive force about double that which he can exert 
continuously ; hence, when short grades occur steeper 
than the general grades of the road, loads may often 
be taken over them much heavier than could be carried 
if the steeper grade prevailed upon the road. 

Art. 4. Desirability of Various Road 
Surfaces. 

The desirability of a road surface for any particular 
use depends both upon its fitness for the service re- 
quired of it and upon its durability in use. 

Upon a country road, the problem of improvement 
ordinarily consists simply in providing the hardest and 



lO A TEXT-BOOK ON ROADS AND PAVEMENTS. 

most durable surface consistent with an economical 
expenditure of available funds, the object being to 
lighten the cost of transportation by reducing the 
resistance to traction, and to render travel easy and 
comfortable. 

Upon city streets, however, several other factors 
may be of importance in the design of highway im- 
provements. 

The comfort both of those using the street and of 
the occupants of adjoining property will be largely 
affected by the freedom of the surface from noise and 
dust. 

The safety of the pavement in use, its effect upon 
the health of residents of the locality, and its economic 
value must in each case be considered. 

To adjust to the best advantage these various ele- 
ments, frequently quite discordant with each other, is 
a matter which can only be accomplished by the exer- 
cise of good judgment. Local conditions and necessi- 
ties must always be considered — such as the difficulties 
of drainage, the availability of various materials, the 
nature of the traffic to be carried, and the needs of the 
business or property interests of the neighborhood. 
Thus, for heavy hauling of a large city, the durability 
and resistance to wear of the pavement may be the 
paramount consideration ; for an office district, quiet 
may be very important ; for the lighter driving of a 
residence street, the elements of comfort and health- 
fulness may properly be considered as of greater force 
than the purely economic ones ; while in all of the 
cases the necessary limitation of first cost will largely 
determine what may or may not be done. 



general considerations. ii 

Art. 5. Economic Value. 

The determination of the economic value of any 
proposed road or street improvement is always a 
matter of difficulty, as it embraces so many items 
which cannot be exactly evaluated. The factors to be 
considered in this connection are : 

1. Cost of construction. 

2. Cost of maintenance and repairs. 

3. Cost of conducting transportation. 

4. Effect upon land values or business interests. 
For the purpose of comparing various pavements, 

or of considering the advisability of any proposed im- 
provement, we may sum the interest on the cost of 
construction with the annual charges representing the 
other items, and find which improvement will make the 
total annual cost a minimum or annual benefit a maxi- 
mum. This process, in any case in practice, simply 
amounts to a use of the judgment, having properly in 
view the various interests to be affected, as to what 
expense may legitimately be allowed in order to secure 
a certain benefit. The outlay is usually quite tangible 
and easily estimated, while the advantages cannot be 
directly estimated and are often overlooked. It must 
not, however, be supposed that they have no financial 
value, or that the pavement which can be constructed 
and maintained for the least money is necessarily the 
most economical to use. 

The cost of construction must, of course, include 
everything connected with the original construction 
of the road and all necessary expenses leading to the 
improvement under consideration. 

The cost of maintenance and repairs includes an esti- 



12 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

mate of the average cost of keeping the road in good 
condition over a term of years, taking into account the 
necessity of renewing the surface at the expiration of 
the Hfe of the pavement, the cost of cleaning and 
sprinkHng, and such minor repairs as may be neces- 
sary from time to time to maintain a uniformly good 
surface. 

An approximate estimate upon these points may 
usually be made by examining the records of the same 
kind of construction under similar conditions else- 
where. The cost of maintenance of each kind of 
pavement varies widely in different localities and 
under differing treatment, and no general rules can be 
stated as to the relative costs of the various systems. 

All road surfaces will require maintenance, the same 
as any other class of engineering constructions sub- 
jected to wear in use ; and as a rule the cost of main- 
tenance will be less as the care used in keeping the 
surface always clean and in good condition is greater. 

The cost of transportation is affected by the nature 
and condition of the road over which the trafific must 
pass, both because the resistance to traction offered by 
the surface determines the load that may be hauled 
over it, and because the roughness of the surface 
serves both to limit speed and to cause wear upon 
horses, harness, and vehicles. The evaluation of these 
items is a matter of difficulty, on account of the practi- 
cally indeterminate nature of the data upon which they 
should be based. 

A rough idea of the relative cost of transportation 
over different road surfaces may sometimes be obtained 
by observing or estimating the extent and nature of 
the trafific that is likely to pass over the road and esti- 



GENERAL CONSIDERATIONS. 1 3 

mating the cost of carrying this traffic over each sur- 
face. The portion of the traffic which consists in 
hauHng maximum loads will be directly affected by 
differences in tractive resistances ; the number of loads 
necessary to move the traffic, and hence the cost, 
being, for this portion, approximately proportional to 
the resistance. For the lighter portion of the traffic 
the greater speed with a smooth surface and easy 
grades will be of value in the saving of time, although 
difficult to state in money values. 

The effect of a smooth surface is also very appre- 
ciable in the cost of wear and tear upon horses, vehi- 
cles, and harness. The value of this item is variously 
estimated, and probably ranges from one to ten cents 
per mile travelled. 

Earth roads, in good condition, and wood pavements 
seem most favorable to horses, although asphalt and 
broken-stone roads are commonly considered most 
advantageous as to general wear. Brick would not 
differ greatly from asphalt. On earth roads in poor 
condition the wear is severe, and on stone blocks it is 
estimated to be three or four times as great as on 
asphalt. The financial value of the saving in this wear 
and tear is difficult to ascertain, but it is undoubtedly 
sufficient to make it an important item in the cost of 
highway transportation. 

Land Values. — The effect of highway improvements 
upon the value of adjoining property is dependent 
upon the nature of the uses to which the property may 
be put, and the extent to which various characteristics 
of the road surfaces, such as dust or noise, may affect 
the occupations or comfort of the occupants. A 
pavement may thus sometimes have a direct effect 



14 A TEXT-BOOK ON ROAt)§ AND PAVEMENTS. 

upon rental values. In general, however, the effect is 
difficult to estimate, although it is commonly recog- 
nized in the practice of assessing a portion of the cost 
of improvements against abutting property. 

The value of comfort, convenience, safety, and 
healthfulness to a community, as affected by the con- 
dition of their roads and streets, cannot readily be 
stated in figures ; but they have a money value, both 
in their effect upon the general life and business of the 
community and in the attraction presented to outside 
business enterprises or home-seekers. 

Art. 6. Healthfulness. 

The effect of a pavement upon the health of the 
residents of its locality will be affected by the tendency 
of the materials composing it to decay, by its permea- 
bility, and by its degree of freedom from noise and 
dust. 

The permeability of a road surface is important on 
account of the tendency of surface-water and refuse 
matter to penetrate and saturate it, and thus cause it 
to become dangerous to health. A continuous sheet 
pavement is the most desirable in this particular, and 
a block pavement with open joints the least so. When, 
however, the joints of a block pavement are properly 
cemented, the pavement may be made nearly imper- 
vious. If the material of which the pavement is com- 
posed be permeable, it may gradually become saturated 
with street refuse, even though the joints be made 
tight, and where the material is liable to decay it may 
of itself become obnoxious to health. 

Both these objections are raised to the use of wood 



GENERAL CONSIDERATIONS. 1 5 

pavements, and probably in many cases with justice. 
This is a matter, however, concerning which authorities 
differ. The extent of the danger to health involved 
in the use of wood for pavements in any particular 
case probably depends largely upon the wood selected 
for use, and the method of construction adopted. It 
is at least questionable whether the permeability of the 
material used for pavements is in practice ever as ob- 
jectionable on the ground of health as that caused 
by open-joint construction of block pavement, even 
though the material of the blocks be impervious to 
moisture. 

The noise made by traffic upon a pavement is impor- 
tant not only because of its effect upon the comfort of 
the people using it or living adjacent to it, but also 
because to it are frequently attributed many nervous 
disorders to which people in some cities are subject. 

Stone-block pavements are the most objectionable 
in this particular, causing a continual roar, due both to 
the rumbling of wheels over them and the blows of the 
horses* feet upon them. Upon asphalt the noise is only 
that due to the horses' feet, giving a sharp, clicking 
sound. Upon wood the horses produce no appreci- 
able sound ; but wheels give a dull rumble, generally 
considered the least objectionable of any of the noises 
made by the more common pavements. The noise of 
wood pavements is diminished by making the joints 
between blocks small. A brick surface gives a combi- 
nation of the sounds of wood and asphalt, the clicking 
being much less sharp than on asphalt, and the rumble 
less noticeable than on wood. On any block pave- 
ment the noise is lessened as the foundation is made 
more firm and the joints more close and well cemented. 



1 6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

An earth or broken-stone road is usually less noisy 
than any of the hard pavements. 

The giving off of dust by a pavement under the 
action of traffic is also objectionable on the score of 
health as well as of comfort. All pavements produce 
more or less dust, the amount depending more upon 
the method of construction and care used in forming 
the surface and filling the joints than upon the material 
of the pavements. For the most part, however, the 
presence of dust is dependent rather upon the main- 
tenance, cleaning, and sprinkling of the pavement than 
upon its nature, and the dirt upon the surface of a 
hard pavement is usually carried there from the out- 
side and not due to the pavement. 

Earth and broken-stone roads wear rapidly, and 
make dust freely in dry weather, requiring frequent 
sprinkling and cleaning to keep the road clear of it, 
and are on this account objectionable for use on the 
streets of towns under any considerable traffic. 

Art. 7. Safety. 

The safety of a road surface depends upon the foot- 
hold afforded by it to horses under normal conditions;, 
and also upon the degree of slipperiness that it may 
take in wet weather, or under the influence of ice and 
snow in winter. 

A dry earth road in good condition gives the best 
and surest foothold, with broken-stone and gravel 
roads nearly as good. 

The relative safety of the various pavements used in 
city streets is a matter upon which there is consider- 
able difference of opinion amongst authorities. Local 



GENERAL CONSIDERATIONS. 1 7 

conditions affect the pavement in this regard to an im- 
portant degree. The dampness of the climate, the 
shade from buildings, the cleanliness of the streets, 
and the prevalence of snow and ice in winter are all 
important. 

Statistics upon the question of relative safety of 
wood, asphalt, and granite have been collected by 
Capt. Greene in this country and by Col. Haywood 
in London, the attempt being made to determine 
the number of miles travelled by horses upon each 
kind of pavement to each accident due to slipperi- 
ness. 

The results of Col. Haywood seem to show that 
of the three wood is the safest and granite the most 
dangerous, while the results of Capt. Greene show 
asphalt to be the best and wood the worst in this 
particular. 

Col. Haywood's observations were all taken on 
London streets, and are as follows : 

Miles travelled to each fall on 





Granite. 


Asphalt. 


Wood. 


In dry weather, 


78 


223 


646 


" damp " 


168 


125 


193 


" wet 


432 


192 


537 


All observations. 


132 


191 


330 



The observations were made when dry weather 
prevailed, and therefore are somewhat unfavorable to 
granite, which is safest when wet. 

Capt. Greene's observations were made in several 
American cities, and showed the distance travelled to 
each fall to be, on granite 413 miles, on asphalt 583 
miles, and on wood 272 miles. The observations on 



l8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

wood in this series were too few to give a reliable in- 
dication, and it is to be observed with regard to all oi 
them that slipperiness is largely affected by the con- 
dition in which the surface is maintained, and it is 
therefore difficult to draw any general conclusions 
which would fit all cases. 

All hard pavements are slippery when muddy and 
wet, and cleanliness is the necessary condition of 
safety. 

Wood and asphalt, if clean, are least slippery when 
dry and most so when simply damp. Granite, after 
the surface becomes worn and polished, is most slip- 
pery when dry and least so when wet. 

Under a light fall of snow both wood and asphalt 
become very slippery, and in freezing weather wood 
sometimes becomes slippery through the freezing of 
the moisture retained by it. 

No statistics are available as to the safety of brick 
pavements, but it is thought a desirable material in 
this respect. 

It may also be remarked, that the danger of a horse 
falling upon any pavement depends very largely upon 
the training of the animal and whether he be accus- 
tomed to the particular surface in question. 

Art. 8. Durability of Various Surfaces. 

The durability of a road or pavemjnt is dependent 
upon so many, circumstances connected with local con- 
ditions, the nature of the traffic, methods of con- 
struction, and efficiency of maintenance, that any 
comparison of the various kinds of pavement in this 
respect is difficult and likely to be misleading. 



GENERAL CONSIDERATIONS. IQ 

The qualities which especially affect the durability 
of the road may be partially enumerated as follows : 

(i) The hardness and toughness of the material com- 
posing the surface, upon which depends the resistance 
of the surface to the abrading action of the wheels and 
horses' feet passing over it. 

(2) The firmness of the foundation, which serves to 
distribute the loads over the road-bed, and keep the 
surface uniform. 

(3) The drainage of the road-bed, which can only 
properly sustain the loads which come upon it when it 
is dry. 

(4) The permeability of the surface, which should 
form a water-tight covering to serve the purpose of 
keeping the foundation and road-bed in a dry con- 
dition. 

(5) The resistance o( the materials of the pavement 
to the disintegrating influences of the atmosphere, and 
to the action of the weather. 

The relative importance of these various factors, in 
any particular case, depends largely upon the nature 
and extent of the traffic which is to pass over the 
pavement. 

The amount of traffic to which a street is subjected 
is usually estimated in terms of tons per foot of width 
of street, by observing the number of teams passing a 
given point during certain times, classifying them, and 
assigning an average value of load to each class. The 
wear of the surface will naturally be somewhat propor- 
tional to the amount of traffic. The life of a pave- 
ment is, however, affected by other conditions, and 
hence cannot always be inferred from the amount of 
traffic. 



20 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Traffic may also be classified according to its nature 
as heavy or light, depending upon the weight of indi- 
vidual loads which are carried. It is the heavy loads 
borne upon narrow wheel-tires that do the greatest 
damage to a pavement, and hence the nature rather 
than the amount of traffic determines the character of 
pavement necessary. 

Granite blocks, where a firm unyielding foundation 
is employed, give the hardest and most durable surface 
of any of the common pavements. This is especially 
the case under very heavy loads. 

Asphalt and brick rank next to stone, and when 
well constructed are satisfactory under any but the 
heaviest traffic. The relative durability under wear of 
brick and asphalt is a matter of doubt, both materials 
being subject to considerable variations in quality, 
and showing varying results in different localities, due 
both to differences in the quality of the material and 
in the methods of construction. 

Wood is less durable and only suitable for com- 
paratively light traffic, unless its other advantages be 
considered worth the high cost of maintenance under 
heavier traffic, as has been the case in London, where 
wood has been largely used u;ider traffic which required 
its renewal every four or five years. 

Broken stone wears rapidly under moderately heavy 
traffic, and should be employed only on suburban 
streets or country roads used mainly for light driving 
or a small amount of traffic. 

The durability of any pavement also depends largely 
upon the system employed for maintaining it, and 
upon its being kept clean. Cleanliness is specially 
important with wood, asphalt, and broken stone. 



GENERAL CONSIDERATIONS. 21 

Brick or stone blocks are not so much injured by- 
neglect. 

The wear of a pavement also depends largely upon 
the smoothness of the surface, as the impacts to which 
the material is subjected are produced by irregularities. 
So that the most durable material may not always give 
the greatest resistance to wear. 



CHAPTER II. 
DRAINAGE OF ROADS AND STREETS. 

Art. 9. Necessity for Drainage. 

The road-bed, usually formed of the natural earth 
over which the road or pavement is to be constructed, 
must always carry the loads which come upon the 
road surface. Where an artificial road surface or 
pavement is employed, the earth road-bed is protected 
from the wear of the traffic, and the wheel loads com- 
ing upon the surface are distributed over a greater 
area of the road-bed than if the loads come directly 
upon the earth itself ; but the loads are transferred 
through the pavement to the road-bed, and not sus- 
tained by the pavement as a rigid structure. 

The ability of earth to sustain a load depends in a 
large measure upon the amount of moisture contained 
by it. Most earths form a good firm foundation so 
long as they are kept dry, but when wet they lose 
their sustaining power, becoming soft and incoherent. 
When softened by moisture the soil may be easily 
displaced by the settling of the foundation of the 
road, or forced upward into any interstices that may 
exist in its superstructure. 

In cold climates the drainage of a road is also im- 
portant because of the danger of injury from freezing. 
Frost has no disturbing effect upon dry material, and 

22 



DRAINAGE OF ROADS AND STREETS. 23 

hence is an element of danger only in a road that re- 
tains water. 

In order, therefore, that the loads may be uniformly 
sustained, and the surface of the road kept firm and 
even, it is evidently of first importance that the road- 
bed be maintained in a dry condition. This may be 
accomplished by the use of an impervious road cover- 
ing, by proper underdrainage, or by a combination of 
the two, as may be necessary in any particular case. 

An impervious surface is always desirable, not only 
as a means of keeping the road-bed dry, but also as a 
protection to the pavement itself against the disin- 
tegrating action of water and of the weather upon 
the materials of the surface. Such a surface is not, 
however, always practicable, and other means must 
often be used to free the road from water. 

The necessity for underdrainage in any case de- 
pends upon local conditions, the nature of the soil, and 
the tendency of the site to dampness, as well as the 
permeability of the surface. 

The object should be as far as possible to prevent 
water from reaching the road-bed, and to provide 
means for immediately removing such as does reach it 
before the soil becomes saturated and softened. 

Art. 10. Surface Drainage. 

The drainage of the surface of a road is provided for 
by making the section higher in the middle than at the 
sides, with ditches or gutters at the edges of the road 
along which the water is conducted until it may be dis- 
posed of through some side channel. 

The slope necessary from the middle to the sides of 



24 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the road to insure good drainage depends upon the 
nature of the covering, being less as the road surface 
is more smooth and less permeable to water. It varies 
from about i in 20 or i in 30 for broken stone to i in 
40 or I in 60 for various classes of pavement, and for 
asphalt sometimes as low as i in 80. 

The form of section used is commonly either a con- 
vex curve, approximately circular, or it is made up ot 
two plane surfaces sloping uniformly from the middle 
to the sides in each direction, and joined in the middle 
by a small circular arc. There has been considerable 
dispute among engineers as to which of these forms is 
most desirable, although the general preference seems 
to be given the plane section. It is not usually a 
matter of special importance, provided the section 
used is not too flat at the middle for good drainage, 
and not too steep at the gutters for safety. In 
places where surface-water must be carried for con- 
siderable distances in gutters at the side of the road, 
and provision must be made for a considerable flow, 
the gutters may be deepened by increasing the slope 
0/ the surface at the sides, or rounding off as much 
as possible without making the slope too steep for 
safety. 

The road should also have a certain longitudinal 
slope in order that the water may flow freely in the 
gutters. This slope should be at least i in 200 in 
most cases in paved streets, and somewhat greater — 
about I in 100 to I in 120 — on broken-stone or earth 
roads. Where longitudinal slopes are steep, some pro- 
vision must be made to prevent the wash of the gut- 
ters, and in such places it is specially desirable to take 
the water from the gutters as frequently as possible, 



DRAINAGE OP' ROADS AND STREETS. 



25 



in order to make the gutter flow small. This may 
often require, where no sewers exist, the laying of 
a special pipe underground for the purpose. 

On country roads the disposal of surface-water is 
not usually a matter of difficulty, as it can be carried 
along the road and run into the first convenient cross- 
channel. 

In towns the most satisfactory method of disposing 
of surface drainage is through a system of storm 
sewers, the water collected in the gutters being emptied 
at frequent intervals into the sewers and thus quickly 
removed from the surface of the street. In the ab- 
sence of such a system it may often be necessary to 
lay pipes, connecting with the nearest natural channel, 
to relieve the gutters. In such cases catch-basins 
should always be placed at the entrance to the pipe 
to prevent it getting clogged by the dirt which may 
be washed in from the gutter. On 
lines of pipe of considerable length, 
catch-basins should also be intro- 
duced at intervals, to allow the 
accumulated sediment to settle and 
be removed. 

Fig. 3 represents a basin of this 
kind. It may be formed for small 
pipes, of a length of pipe set on 
end with the lower end closed, or 
where necessary a box built of 
masonry may be employed. 

In all cases it is important that the water which 
falls upon the surface should be gotten rid of as soon 
as possible, for so long as it remains upon the road it 
it is an element of danger, both from its tendency to 




Fig. 3. 



26 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

wash the surface, and from its Hability to penetrate 
into the road and thus cause disintegration or settle- 
ment. The best method of removing this water in 
any particular case must be determined by a careful 
study of local conditions, and its final disposal in the 
case of the streets of a town is a special problem re- 
quiring careful treatment. 

Art. II. SUBDRAINAGE. 

The drainage of the sub-soil of a road-bed may be 
directed either to the removal from the road-bed of 
water that percolates through the road covering, or to 
the prevention of sub-surface waters from reaching 
and saturating the road-bed. 

The necessity for subdrainage, and the method to 
be employed in any case, depends upon whether the 
soil over which the road is being constructed is natu- 
rally wet or dry, and whether the road-bed is so situ- 
ated and formed as to give it natural drainage. 

Where artificial subdrainage is necessary the drains 
should be located, in so far as possible, with a view to 
cutting off the supply of water before it reaches the 
road-bed. To accomplish this to the best advantage 
the local conditions must be observed, the sources of 
this supply determined, and the nature of the under- 
flow, if any exist, considered. 

In many situations, particularly when the site of the 
road is low and naturally damp in wet weather, it may 
be advisable to place a longitudinal drain under each 
side of the road. Such a construction is shown in 
Fig. 4, which gives a section of a macadamized country 
road with tile side-drains. 



DRAINAGE OF ROADS AND STREETS. 



27 



Frequently, as in many cases of a road along a side 
slope, there is a well-defined flow of sub-surface water 
from one side to the other, and in such case the water 





Fig. 4. 

may perhaps be intercepted by a single longitudinal 
drain on the side of the roadway from which the 
water comes. An example of this is shown in Fig. 5, 



^ 



Fig. 5. 

which represents a macadamized village street with 
stone curb, gutters, and sidewalks. 

In other cases, where the subsoil is of a very reten- 
tive nature, or where the natural slope of the land is 
in the direction of the length of the road, cross-drains 
leading into a longitudinal side-drain or into side- 
ditches may be expedient, and sometimes, especially 
upon narrow country roads, a single longitudinal drain 
under the middle of the road may give the best re- 
sults, serving both to remove sub-surface water and 
that which percolates through the road surface. Fig. 
6 shows such a road, representing an ordinary earth 
road with a tile centre-drain. Fig. 20 also represents 
a stone centre-drain as sometimes used under a broken- 
stone road over wet ground. 



28 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

These longitudinal drains should be arranged to 
empty as frequently as possible on country roads into 
the natural drainage-channels, or in towns into sewers 
arranged to convey the water rapidly away. 

In general, systematic underdrainage will not be 
necessary except in localities where the ground is natu- 
rally damp from lack of natural drainage, or where an 




,^ 



Fig. 6. 

underflow creates a tendency to wetness in the sub- 
soil. In some localities, however, upon country roads, 
where an impervious surface is not employed and the 
soil is one that absorbs and retains water, it may be 
necessary to provide subdrainage to remove water 
that passes through the road surface. This is most 
commonly done by a series of shallow cross-drains or 
by a single longitudinal one in the middle of the road. 
In a town where sewers traverse the streets subsoil 
drainage is easily arranged for in connection with the 
sewers. Frequently blind-drains or stone-drains are 
constructed underneath or alongside the pipes. In 
other cases good drainage is secured by drains under- 
neath the curb or gutter, which are connected with the 
sewers. 

Art. 12. Kinds of Soil. 

The material of which a road-bed is composed is 
important because it determines to a large extent 



Drainage of roads and streets. 29 

whether artificial drainage is necessary, and also what 
method should be adopted for securing drainage. 

Soils differ in their power to resist the percolation 
of water through them, in the rapidity and extent of 
their absorption of water with which they come in con- 
tact, in the extent to which moisture renders them soft 
and unstable, and in their power of retaining moisture. 

A light soil of a sandy nature usually presents little 
difficulty in the matter of drainage, as, while it is easily 
penetrated by water, it is not retentive of moisture, 
which passes freely through it without saturating it 
unless prevented from escaping. 

If the natural drainage, therefore, have a fall away 
from a road-bed formed of such material it will usually 
need no artificial drainage, and where subdrains are 
necessary they may be relied upon to draw the water 
from the soil to a considerable distance each side of 
the drain. 

A nearly pure sand is more firm and stable, under 
loads, when quite damp than if dry, although a fine 
sand saturated by water which is unable to escape 
may become unstable and treacherous. 

Clays usually offer considerable resistance to the 
passing of water through them, and are very retentive 
of moisture. As a rule, however, a clay soil does not 
absorb water readily, and requires that water be held 
for some time in contact with it in order that it may 
become saturated, although when saturated it is the 
most unstable of soils. A clay that when dry will 
stand in a vertical wall and support a heavy weight 
when wet may lose all coherence and become a fluid 
mass. When water comes in contact with a bed of 
such clay, the outside becomes saturated and semi- 



30 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

fluid before the moisture penetrates into it sufficiently 
to even moisten it a few inches from the surface. 

A clay soil is, therefore, always difficult to drain by 
removing the water after it has soaked in, or by per- 
mitting it to pass through the road-bed to the subdrains 
beneath. Drainage, in such cases, may often be so 
arranged as to prevent water from standing against 
the road and thus prevent it from becoming saturated. 
As the clay is comparatively non-absorptive, the water 
which may come upon its surface, if allowed to escape 
at once, will not penetrate into it, and hence will not 
cause softening. 

A heavy silt formation is sometimes met with which 
is even more difficult to drain than a true clay. It is 
nearly as retentive of moisture as a clay, strongly re- 
sisting the passage of water through it, but at the same 
time absorbs water quite freely when in contact with it. 

Between the extremes mentioned above there are 
a great number of varieties of soil which possess to a 
greater or less extent the characteristics of either or 
both, and gradually merge the one into the other. In 
applying a system of drainage in any case, careful 
attention should always be given to the characteristics 
of the soil, as determining very largely the treatment 
to be used. 

In pervious, sandy, or gravelly soil drains may often 
be effective for a distance of 30 or 40 feet through the 
soil, while with a less pervious retentive clay the drain 
may not act effectively more than 8 or 10 feet on each 
side. 



drainage of roads and streets. 3i 

Art. 13. Types of Drains. 

For the purpose of draining the subsoil of the road- 
bed the drains used may be either open ditches at the 
sides of the roads or porous covered drains. 

Open ditches are sometimes used on country ropds. 
They are usually placed at the extreme edges of the 
road, and must be deep in order to be effective. Being 
so far from the travelled portion of the road, they can 
only act satisfactorily as subdrains where the soil is 
pervious and easily drained. 

In other cases, where side-ditches are employed, 
covered cross-drains must be introduced to carry the 
water from the middle of the road to the ditches. Fig. 
7 shows a section of a country road drained by side- 




FiG. 7. 

ditches. Where such ditches are employed the slope 
of the sides should be made as gradual as possible, at 
least i^ or 2 horizontal to i vertical, in order to dimin- 
ish the danger of the washing of the banks, as well as 
the liability to overturning of a vehicle over the edge. 
Covered underdrains are to be preferred to open 
ones for this use, and are more commonly employed 
where efficient subdrainage is attempted. These 
drains must be so arranged that they may be read- 
ily penetrated by the water without becoming clogged 
by earth washing into them. The types of drains 
most commonly employed for this purpose are known 
as blind drains, box or stone drains, and tile-drains. 




32 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

For short lengths, such as transverse drains intended 
to take the water from the subsoil into the side ditches 
or drains, blind drains may frequently be economically 
employed. They consist simply (as shown in Fig. 8) 

of ditches cut into the soil 
and filled with rounded 
stones 3 to 6 inches in di- 
ameter. Angular stones are 
not desirable for this pur- 
pose, as the object is to 
leave openings into which 
the water may penetrate 
without difficulty, and thus 
^^' * be led away. The top of 

the stones must be covered over in some way before 
filling in earth above in order to prevent the earth from 
washing down and choking the drain. This is some- 
times accomplished by using smaller stones at the top, 
covered by a layer of coarse gravel. A layer of straw 
or brush, or of sod turned roots upward to retain the 
earth until it becomes thoroughly compacted, is a 
common and effective method of protecting these 
underdrains. 

Stone-drains are commonly employed where stone is 
plenty and cheap. They usually consist of rectangular 
or triangular boxes formed of flat stones or bricks at 
the bottom of a trench, which is then filled as in a blind- 
drain so as to give ready access for water. 

Figs. 9 and lo show sections of stone-drains as com- 
monly constructed of rough field-stones. The form 
given in Fig. 9 is commonly known as a box drain. 

Tile-drains are probably in general the most con- 
venient and efficient for subdrainage. They are made 



DRAINAGE OF ROADS AND STREETS. 



33 



of round, or U-shaped, unglazed drain-tile, laid, as in the 
last case, at the bottom of a ditch filled with round 
stones. 

Fig. 1 1 shows the section of a tile-drain as commonly 
constructed. 

The tiles are usually set ,end to end in the trench, 





Fi6. 9. 



Fig. 10. 



being held in place by small stones braced under- 
neath. 

The joints are thus left open to permit of the free 
entrance of water. Collars for the joints may be ob- 
tained and are sometimes used 
where thought necessary to keep 
larger material from washing into 
and obstructing the tile. These 
collars are rings of pipe into which 
the ends of two adjoining sections 
of the tile may be fitted, and they 
thus serve also to hold the tile in 
line. 

The filling of the trench above 
the tile, as in the other drains, 
should be arranged with a view to maintaining a 




Fig. II. 



34 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

porous structure through which water may easily 
pass. Sometimes flat stones are laid over the tile 
resting with one edge on the bottom of the trench 
and meeting above at the middle so as to form an 
additional protection to keep any earthy matter from 
choking the entrance to the tiles. 

All of these drains should be deep enough to escape 
freezing. 

The mouth of a tile-drain should also be protected 
in some manner, as the porous tile is apt to be broken 
and destroyed by frost when saturated. In some cases 
the tile-drain is made to discharge through a short 
length of stone-drain, or through a section of salt- 
glazed sewer-pipe, which will not be injured by freez- 
ing. 

It is desirable in all cases to protect the mouths of 
underdrains with a netting of some kind to prevent 
the entrance of vermin, which may clog the openings 
with their nests. 

The slope of a porous drain may vary from about i in 
40 to I in 100. In case a steeper slope be necessary, a 
foundation or paving should be placed in the bottom 
of the trench, which is otherwise liable to be eroded by 
the current that may be produced. 

Art. 14. Culverts. 

Culverts are commonly required in road construction 
for carrying under the road the small streams Avhich 
may be crossed by the road, or sometimes for carrying 
the water collected in the gutters or ditches on the 
upper side of the road to the lower side. 

The waterway provided by a culvert must, for 



DRAINAGE OF ROADS AND STREETS. 35 

safety, be sufficiently large to pass the maximum flow 
of water that is likely to occur, while for economy it 
must be made as small as may be without danger. 

The maximum flow of a stream depends upon a 
number of local conditions, most of which are very 
difficult of accurate determination. These are : the 
maximum rate of rainfall ; the area drained by the 
stream and its position ; the character of the surface 
drained ; and the nature of the channel. 

The maximum rate of rainfall varies in different 
localities, and differs in the same locality from year to 
year. It is commonly taken at about an inch an hour. 
This is sometimes exceeded for a very short time and 
over a small area, but is usually a safe value for a 
watershed of any considerable area. 

The approximate area of the watershed drained by 
a stream is readily found, and its form is also impor- 
tant as determining the distance the water must flow in 
reaching the culvert under consideration, and to some 
extent regulating the rate at which the water falling 
upon the area will reach the culvert. 

The maximum flow of a stream is also affected by 
the physical characteristics of the watershed. The 
permeability of the surface largely determines what 
portion of the rainfall shall reach the stream ; while the 
slope of the surface, its evenness, and its vegetation 
have an effect upon the quickness and rate with which 
the rainfall is received by the stream. 

The determination of the maximum flow to be ex- 
pected in any case from an examination of the locality 
is therefore possible only as a very rough approxima- 
tion. A number of formulae have been proposed for 
such estimation, the use of which for the case of an 



j6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

ordinary culvert simply amounts to estimating the 
quantity of water which would fall on the watershed in 
the heaviest probable rain, and judging as well as pos- 
sible from local conditions how much of it may arrive 
at one time at the culvert. In some cases where a 
more accurate determination is desirable it may be 
advisable to measure the flow of the stream at high 
water, and form an idea from such measurement as to 
what may be expected at a maximum stage. 

The amount of water that will pass a culvert in a 
given time depends upon the form of the section, the 
smoothness of its interior surface, its slope, and the 
head under which the water is forced through. A 
well-constructed culvert may be considered in comput- 
ing its capacity as a pipe flowing full. Other culverts 
or bridges must be treated as open channels. 

Prof. Talbot gives (Selected Papers C. E. Club, Univ. 
of Illinois, 1887-8) a formula for the rough determina- 
tion of area required for waterway, derived from 
experience : 



Area waterway in feet ^= C V (drainage area in acres)'. 

€^ is a coefficient depending upon local conditions. 
For rolling agricultural country subject to floods at 
time of melting snow, and with length of valley 3 or 4 
times the width, C ^=\. When the valley is longer, 
decrease C, If not affected by snow and with greater 
lengths, C may be taken at ^, \, or even less. For steep 
side slopes C should be increased. 

For most cases in practice the size of waterway 
required may be determined from the knowledge which 
usually exists in the vicinity regarding the character of 



DRAINAGE OF ROADS AND STREETS. 37 

a stream, from the sizes of other openings upon the 
same stream, or from comparison with other streams 
of like character and extent in the same locaHty. 
Where data of this kind do not exist, careful exami- 
nation of water-marks on rocks, the presence of drift, 
etc., may be made to determine the height to which 
water has previously risen. 

For small flow of water box culverts of stone or pipe 
culverts are commonly employed. Wooden box cul- 
verts are also sometimes used, constructed of planks or 
heavy timbers, but should be avoided in so far as pos- 
sible on account of their perishable character, and con- 
sequent lack of economy. 

Pipe culverts are the most efficient in use, and as 
they can now be constructed quite cheaply in most 
parts of the country, are coming into very general use. 
The efficiency of a pipe culvert may frequently be 
greatly increased by arranging it to discharge under 
a considerable head at times of unusual flood. This 
requires that the water shall freely flow away below 
the outlet, and that the surface of water above the 
culvert may stand higher than the head of the pipe. 

Pipe culverts may be constructed either of salt- 
glazed vitrified sewer-pipe, or of iron water-pipe. 
The iron pipe possesses greater strength, and is pref- 
erable where a firm foundation is not easily obtained, 
as it is not so easily broken by any slight settlement. 

In laying pipe culverts, they should be placed on a 
solid bed, and the earth be well tamped about them. 
It is desirable to have the bottom of the trench exca- 
vated to fit the lower part of the pipe, depressions 
being formed for the sockets. It is necessary in every 
case that the pipe be firmly and uniformly supported 



38 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

from below, in order that the culvert may not be 
broken by settlement, which is especially likely to 
occur in new work. 

It is desirable that the joints in the pipe be made 
water-tight, especially where the culvert is likely to flow 
full or under pressure, as any water escaping through 
the joints will tend to cause a wash beneath the pipe 
and undermine the culvert. Joints are commonly 
filled with clay. Where strength is needed the use of 
hydraulic cement mortar is preferable, and sometimes 
the small end of the pipe is roughened on the outside 
and the socket on the inside in order that the cement 
may hold more firmly. 

Care should be taken that the culvert have sufificient 
slope and be so placed that water may not stand in 
it, in order to prevent injury from freezing, and the 
top of the culvert pipe should be at least two feet 
below the road surface to avoid crushing. 

The ends of pipe culverts should be set in masonry 
walls to give protection against the washing of the 
face of the embankment, hold the ends firmly in place, 
and prevent the entrance of water into the earth on 
the outside of the pipe. 

These walls to give efficient protection must be of 
substantial construction, going down to a solid founda- 
tion below the bed of the stream. They may be built 
of rubble masonry, and should be laid up in hydraulic 
cement mortar. Such construction is represented in 
Fig. 12. The wall must extend far enough on the side 
to sustain the earth of the embankment from the 
waterway, or wing walls may be used extending up 
stream for this purpose. The waterway should be 



DRAINAGE OF ROADS AND STREETS. 



39 



paved above the culvert far enough to prevent scour- 
ing at the base of the wall. 

For quite small streams the walls may sometimes 
be omitted if the face of the embankment about the 
entrance to the pipe and the waterv/ay for some dis- 
tance above and below be riprapped. Where it is 
necessary to economize in the cost of construction, 
this method is preferable to the use of very light end 
walls. 

On streams too large for a single pipe it is often 
economical to lay two or three pipes side by side, 




imummmminniv 




ttvttvwmmniimniii 




Fig. 12. 



rather than to construct an arch or the open way of a 
bridge. In laying large pipes it is usually advisable 
to place a broken-stone or concrete foundation under 
the pipes throughout their lengths to insure uniform 
support. 

Stone Culverts. — Culverts of stone may be either 
arch culverts or box culverts. Box culverts are usually 
formed of two side walls and a cover. The side walls 
consist usually of rubble stonework laid up dry or in 
mortar, as the case may be. Where the stream to be 



40 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

carried is of small importance, and the capacity of the 
culvert not greatly taxed, dry walls may give satis- 
factory results, but when the culvert is likely to flow 
full at certain times it should be laid up in hydraulic 
cement mortar, and in any case the greater stability 
given by the mortar would be well worth the small 
additional cost. Fig. 13 shows a section of the ordi- 




U w 



Fig. 13. 



nary form of box culvert. The use of head walls and 
paving the waterway for a short distance is necessary 
for these as for pipe culverts. 

Where suitable stone is available, box culverts are 
easily constructed and economical. They are com- 
monly used for openings 2 to 4 feet in width and 
2 to 5 feet in height. The width that may be used 
depends upon the available cover stones. Where the 
allowable width is not sufficient to give the needed 
area of waterway, a double culvert may sometimes be 
used to advantage. This consists of two openings 
with a middle wall to support the covers. 

The culvert's opening should always be large enough 
to admit of a man passing through it for the purpose 



DRAINAGE OF ROADS AND STREETS. 4I 

of cleaning it — at least 18 by 24 inches. The side walls 
should extend downward below the bottom of the 
culvert sufficiently to obtain a good foundation, and 
the thickness required for the side walls usually varies 
from one half to three fourths the height, depending 
upon the pressure likely to come against them. 

In many cases for small work the side walls, instead 
of extending downward, rest upon the paving which is 
extended under them. This gives a somewhat less 
expensive construction, and is often satisfactory on 
good ground. 

The cover stones may be from -J to |^ the span in 
thickness, and should be long enough to have a bear- 
ing upon each side wall of at least one half the thick- 
ness of the wall. 

Arch culverts are used for openings too large to be 
made of the box form or of pipes. The discussion of 
arches and also that of bridges in general is outside 
the proper scope of this book. For ordinary country 
bridges wooden trusses are most commonly employed, 
on account of their comparative cheapness. For short 
span bridges a satisfactory and economical construc- 
tion, which has recently come extensively into use, 
consists in placing a number of wrought-iron eyebars 
across the opening from abutment to abutment at 
short distances apart. Brick arches are then used to 
span the spaces between the eyebars, which are tied 
together with wrought-iron rods, and the roadway is 
then constructed over the bridge in the same manner 
as upon the earth road-bed. 

Concrete culverts may sometimes be used to ad- 
vantage where they can be cheaply constructed. They 
are usually made in oval form, the bottom being first 
formed by ramming the concrete upon the foundation 



42 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

SO as to form a curved channel 4 to 6 inches thick. 
The upper part is then constructed as an arch upon a 
centre, which is left until the mortar has set. For the 
small openings for which these culvert sare employed 
the thickness of concrete in the arch may be from 
J to -J- of the width of opening. The concrete for such 
work should be made of hydraulic cement, in the 
manner employed in constructing the foundations for 
pavements. (See Art. 47.) 

Abutments for small bridges should be laid upon 
solid foundations, and built of hydraulic cement 
mortar, the back of the abutment wall being made 
impervious by coating it with mortar. A common and 
safe thickness of abutment is to make the thickness 
■^-^ of the height. The waterway between abutments 
should be paved to prevent scouring out the founda- 
tions. 

Art. 15. Water-breaks. 

Upon heavy gradients on country roads, continuous 
for any considerable distance, water-breaks are com- 
monly placed at frequent intervals to collect the water 
which flows down the surface of the road and turn it 
into the gutters or side-ditches. They should only be 
used on grade steep enough to make them essential, as 
otherwise they form an obstruction to traffic. They 
consist of broad shallow ditches, and should be arranged 
to carry the water from the middle of the road each 
way to the gutter, thus forming a V with the vertex 
uphill and at the middle of the road. This arrange- 
ment permits teams following the middle of the road 
to cross the ditch squarely. It is desirable that these 
cross gutters be paved to prevent washing during 
heavy showers. 



CHAPTER III. 
LOCATION OF COUNTRY ROADS. 

Art. 1 6. Considerations Governing Location. 

The determination of a line for a proposed road 
involves the examination of the country through which 
the road is to pass with reference to its topographical 
features, the nature and extent of the traffic that it 
may develop, and the local interests that may be 
affected by the position of the road. 

The simplest form that this problem can take is that 
in which two points, as two towns, are to be connected 
by a road for the purpose of providing for a traffic 
between them, the nature and amount of which is 
approximately known. In this case it is only neces- 
sary to examine the topography of the intervening 
country and select the line over which, taking into 
account the costs of construction and maintenance, 
the given traffic may be most economically carried. 

In most cases in practice, however, the problem 
does not have this simple character, and in fact loca- 
tion can seldom be determined by considerations of 
economy alone. The position of the line will be modi- 
fied by local needs, such as the necessity of providing 
for the traffic of villages or farms intermediate between 
the ends of the road, which may often cause deviations 

43 



44 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

from what would be the best line if the interests of 
the terminal points alone were considered. 

Questions of the desirability of various lines for the 
comfort and convenience of travel, and the pleasure to 
be derived from the use of the road, dependent upon 
aesthetic considerations, may also frequently operate 
to change the line from what would seem proper from 
a strictly economic point of view. 

In thickly settled communities, as in most parts of 
the United States, the roads are in the main already 
located, the necessity for the location of new ones 
does not often arise, and when it does occur is usually 
mainly determined by the local needs and requirements 
of traffic. 

The economic considerations involved in the location 
of roads are of two kinds : those relating to the accom- 
modation of traffic, and those relating to its economic 
conduct. The first deals with the necessity of the road 
to the community, the second with the cost of operat- 
ing it. The first involves the general question of the 
advisability of any road, and how it can be placed to 
give the greatest freedom to the movement of travel. 
The question is as to the value of the road to the gen- 
eral community and its location to secure the greatest 
good for the least outlay, without taking into account 
the details of location which may affect the cost of 
transportation. The value of the road as developing 
trade in a town or bringing a farm nearer to market 
would enter into consideration. The accommodation 
of traffic requires that a road be located with a view to 
the convenience of its use by the largest portion of the 
traffic, as well as with a view of developing traffic. 

The position of a road that will best accommodate 



LOCATION OF COUNTRY ROADS. 45 

traffic is that in which, other things being equal, the 
mass of traffic need be moved the least distance in 
reaching its destination ; or, in other words, that for 
which if each ton of freight be multiplied by the dis- 
tance through which it must be moved the summation 
of the resulting products will be a minimum. If there 
be differences in the nature of the routes over which 
the road may be constructed, they may be considered 
as equivalent to changes in the relative effective lengths 
of line for purposes of comparison. 

The ordinary problem of location deals mainly with 
considerations of the second class. It consists for the 
most part in the relocation of portions of old roads, 
of making such changes in position when improving a 
road as may tend to reduce the cost of conducting 
traffic over it, and render it more convenient and 
pleasant for the use of travel, or of determining the 
details of alignment and grade upon a new road which 
is approximately fixed in position by the purpose of 
its construction. 

The most economical location is that for which the 
sum of the annual costs of transportation, the annual 
costs for maintenance, and the interest on the cost of 
construction is a minimum. 

The cost of conducting transportation is affected by 
the rate of grade of the road, the amount of rise and 
fall in it, and the length of the road. The rate of 
grade is important, because it limits the loads that can 
be hauled over the road, or determines the number of 
loads that must be made to transport a given weight 
of freight, as well as fixes a limit to the speed of travel. 
The amount of rise and fall affects the expenditure of 
power required to haul a load over the road. The 



46 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

length of the road has an effect upon the amount of 
work necessary to haul a load over it, the time required 
for a trip, and the cost of maintaining the road surface ; 
each of which, other conditions being the same, is 
directly proportional to the length. 

The cost of construction depends upon the accuracy 
with which the line of the road is fitted to the surface 
of the ground, as determining the amount of earth- 
work and cost of bridges and culverts ; upon the 
character of the ground over which the road is to be 
built, which affects the cost of executing the work and 
determines the necessity for and expense of drainage ; 
and upon the cost of land for right of way. All of these 
items must be considered in any comparison of the 
cost of constructing on various routes. Special care 
should be taken in selecting a line to avoid bad ground, 
such as swamps, upon which construction may be dififi- 
cult and expensive. The availability near the line of 
the road of materials needed for surfacing may also 
become a matter of importance in the cost of construc- 
tion, and have an influence in determining location. 

The relative importance of the various elements af- 
fecting the choice of a line depends upon the nature 
and amount of the traffic to be provided for, and upon 
the character of the road surface to be used. Where 
the traffic is heavy, the importance of reducing the 
co6t of moving it by lessening grades and distance will 
be greater than where the traffic is light, and the cost 
of construction may be correspondingly increased for 
that purpose. If a smooth surface be employed, upon 
which traction is light, the value of reducing grades 
will be greater and the value of reducing distance less 
than with a surface of poorer tractive qualities. 



location of country roads. 4/ 

Art. 17. Length of Road. 

Changes in the length of a road affect all portions of 
the traffic in the same manner, and the expenditure of 
power and loss or gain in time occasioned by them are 
in general directly proportional to their amounts. 

The value of any considerable saving in length may 
usually be considered as equal to the same percentage 
of the whole cost of conducting the traffic that the 
saving in distance is of the whole length. If, therefore, 
a rough estimate may be made of the annual traffic to 
be expected upon a given line of road and of the cost 
of carrying the traffic, this cost divided by the length 
in miles through which the traffic is moved will give 
<ihe annual interest upon the sum that may reasonably 
be expended in shortening the road one mile, or upon 
the value of a saving of a mile of distance ; or di- 
viding by the number of feet of distance will give the 
value of saving one foot. 

It is to be noted, however, that the cost of the work 
of transportation is not necessarily proportional to the 
amount of work done, and consequently this method 
would not be strictly accurate even were the data as to 
traffic and costs readily obtainable. An estimate of 
this character at best amounts to only a rough guess, 
but it may often be of use as an aid to the judgment 
in deciding upon the value of a proposed improvement 
involving a considerable change of length in a road. 

Where the road is so situated and the saving in 
distance proposed is such that it would enable teams 
to make an additional trip per day in the hauling of 
freight, the difference in cost of transportation is quite 
tangible and readily estimated ; but where the traffic is 



48 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of a more indefinite nature, or the saving proposed 
insufficient to admit of additional trips, the value of 
the difference of length depends upon the value to 
other work of the small portions of time of men and 
teams which may be saved by the shorter route — a 
value which exists, but is difficult to estimate. 

There is also a value in the saving of distance due 
to the advantage to the community of bringing the 
various points closer together, such as bringing two 
towns into closer relations or bringing country property 
nearer to markets. The method of considering the 
cost as proportional to the work done will therefore 
probably give a fair idea of the actual economy in any 
saving in the work of transportation. 

The value of reducing distance varies with the 
character of the road surface. As the cost of transpor- 
tation is less over a smooth than over a rough surface, 
on account of the lighter traction, the value of reduc- 
ing distance is also less on the smooth surface. 

The value of saving distance also is greater on a 
road where the ruling gradients are steep than upon 
one with light gradients, because of the greater num- 
ber of loads necessary to move the same traffic. 

The cost of maintenance of a road varies with its 
length, and under similar conditions may be con- 
sidered, like the costs of transportation, to be directly 
proportional to the length of road. 

The saving in cost of maintenance from decreasing 
distance must of course be added to that in cost of 
transportation in order to find the actual value of a 
change of length. 

The value of straightness for a country road is fre- 
quently very much overrated. Considerable deyia- 



LOCATION OF COUNTRY ROADS. 49 

tions from the straight line may often be made with 
but slight increase in length, and there seems to be no 
good reason for insisting upon absolute straightness. 
The error is commonly made of sacrificing grade and 
expense in construction to the idea of straightness 
without the attainment of any considerable saving in 
length. 

It involves in many cases the injury of the beauty of 
the road and of the landscape, with no compensating 
economic advantages. 

Art. 18. Rise and Fall. 

By the amount of rise and fall is meant the total 
vertical height through which a load must be lifted in 
passing in each direction over the road. It is distinct 
from and independent of the rate of gradient. 

The minimum amount of rise and fall is found 
where the rise is all in one direction and the fall in 
the other, each being equal to the difference of eleva- 
tion of the terminal points. Any increase in the rise 
and fall beyond this amount is represented by the rise 
encountered in passing from the higher to the lower 
terminus. It affects the traffic equally in each direc- 
tion, and requires a certain expenditure of power to 
lift the traffic through the given rise in each direction. 

If the cost of developing the work necessary to 
overcome rise and fall be the same as that of develop- 
ing an equal amount of work to overcome distance, thie 
rise and fall may be evaluated in terms of distance, 
and any change in rise and fall may be considered as 
though it were a difference in distance and treated as 
in Art. 17. 



50 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Where the rate of grade is less than the angle of 
repose of the wheels upon the road surface (see Art. 
2) the work necessary to overcome rise and fall will 
be that which will lift the load through a vertical height 
equal to the amount of rise to be considered. When 
the rate of grade is greater than the angle of repose, an 
additional amount of work must be done in applying a 
resistance to prevent the too rapid descent of the vehicle 
in going down the grade. The amount of this work in 
any case equals the work done in lifting the load to a 
height equal to the difference between the actual rise 
of the grade in question and the rise of a grade of the 
same length and a rate equal to the angle of repose. 
Thus on an ordinary earth road whose resistance to trac- 
tion where level is 100 pounds per ton, suppose a grade 
to occur of 8 feet per 100, 1000 feet in length. For 
the road surface we have 100 -^ 2000 = .05, and the 
angle of repose is a 5^ grade. Then 8^ — 5^ = 3^, or 
the brake-power necessary to secure uniform motion, 
is the same as would be necessary to haul the load 
up a 3^ grade, and a grade of 3 in 100 for 1000 feet 
gives 30 feet. The work to be done in holding back 
the load for the looo-ft. grade is therefore the same as 
would lift the load through a vertical height of 30 feet, 
or the fall of 8 feet per 100 for 1000 feet has the same 
effect as 30 feet of rise in the same direction, pro- 
vided brake-power costs the same as animal power. 

The value of rise and fall in terms of distance will de- 
pend upon the nature of the road surface, as the work 
necessary to lift a given load to a given height is a con- 
stant, while the work done in hauling a load over a given 
distance will vary with the resistance offered to traction 
by the surface. Thus, taking the surface as above, the 



LOCATION OF COUNTRY ROADS. 5 1 

work of lifting one ton through a rise of i foot is 2000 
foot-pounds, while with a tractive force of 100 pounds 
per ton 2000 ~ 100 = 20 feet, the distance a ton may- 
be moved on the level surface in developing 2000 foot- 
pounds of work. Therefore i foot of rise or fall may 
be considered as equivalent to 20 feet of level distance, 
and the value of reducing the amount of rise and fall 
may be found from that for reducing distance. 

If the road considered were a first-class Macadam 
road, with resistance of 40 pounds per ton, i foot of 
rise or fall would equal 2000 -f- 40 = 50 feet of distance. 

Art. 19. Rate of Grade. 

The effect of any change in the ruling gradient upon 
a road depends to a considerable extent upon what 
portion of the traffic may be carried in full loads. The 
lighter portions of the traffic are not so seriously 
affected by heavy gradients as the heavy portions, 
although there is an advantage in light gradients for 
any driving. The rate of speed which may be em- 
ployed will be less upon the portions of the road having 
heavy grade, and the time occupied in a trip over the 
road is therefore affected somewhat by the rate of 
grade. 

The desirability of a road for general driving is 
also much influenced by the gradients employed, as is 
that value of the road which has for a basis the effect 
it may exert upon the attractiveness of the locality. 
These things all have a certain financial value, which 
of course it is quite impossible to estimate with any 
degree of accuracy, but which should be considered in 
determining the allowable maximum gradient in any 
case in practice. 



52 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

For heavy traffic, such as the transfer of goods from 
one town to another or the marketing of country prod- 
uce, the Hmitation of load placed upon the traffic by 
the gradient is a matter of importance, the effect of 
which is calculable upon the cost of transportation. 
If in any case the approximate amount of this heavy 
traffic which is likely to be carried in full loads be de- 
termined, the relative costs of its transportation over 
two lines of differing gradient, other conditions being 
similar, will be nearly proportional to the number of 
loads required to move the traffic over each gradient. 

In estimating the value of reducing the rate of grade, 
it may be considered, as in the case of a reduction of 
length, that its value to the community is represented 
by the saving in annual costs of transportation, and 
that the amount that may reasonably be expended in 
increased cost of construction to effect a reduction of 
gradient is the sum upon which this annual saving is 
the interest. 

The length of a road and the amount of rise and 
fall on it determine the amount of work that must be 
done in hauling a load over the road. The rate of 
gradient, on the contrary, does not affect the amount 
of work necessary to move the traffic, but it limits the 
work that a horse may do at one trip. 

The establishment of a proper rate for the ruling 
grade of the line is, therefore, usually the most im- 
portant point in location. In localities where light 
gradients are easily obtained the problem of location 
is greatly simplified. 

By referring to Article 3 the comparative loads that 
a horse may draw up different grades will give some 
idea of the importance of carefully considering the 



LOCATION OF COUNTRY ROADS. JJf 

question of gradient. In nearly all cases in practice 
there is a considerable latitude within which gradients 
may be chosen. It is usually a question of heavier 
gradients as against greater distance and larger first cost 
for the road. It may be remarked that it is only under 
exceptional circumstances that it is either necessary 
or advisable to use a steeper gradient than 55^ on 
the new location of a country road of any importance. 
Grades steeper than the ruling gradient may some- 
times be introduced over short distances without 
impairing the efficiency of the road, as horses are usually 
able to exert for a short time a force much greater than 
they can continuously exert. If the length of grade be 
quite short, 200 or 300 feet, a horse can about double 
his ordinary power in passing it. 

Where long steep grades must be used, it is desirable 
to break them by short stretches of lighter gradients to 
provide resting-places for horses. 

Heavy gradients also have the disadvantage of retard- 
ing traffic in the direction of falling grade, and, as 
suggested in Art. 18, of requiring the expenditure of 
work to hold the load from too rapid descent. 

Art. 20. Examination of Country. 

For the purpose of obtaining the requisite data 
upon which to base the location of a road, it is neces- 
sary that a careful examination be made of the topo- 
graphical features of the country through which the 
line is to pass. The relative elevations of the termini 
of the line and of intermediate points should be 
obtained, and the directions and steepnesses of the 
various natural slopes determined. 



54 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

If a line were to be located connecting points at long 
distances from each other, as sometimes occurs in 
railway location, it would be necessary to study the 
general configuration of the country, noticing the di- 
rection of flow of the streams, and the location and 
elevations of the various passes in the ridges through 
which it might be possible to carry the line. Usually, 
it would be found that the country is composed of a 
series of valleys, separated by ridges, branching in a 
systematic manner from the main watercourse of 
the region, and that the passes in the ridges occur at 
the head of side streams, and especially where streams 
flowing into valleys on opposite sides of the ridge have 
their sources near each other. 

In the location of common roads, however, the prob- 
lem is ordinarily of a less extended nature, and may 
consist in joining two points lying in the same valley, 
or in joining points in adjacent valleys by a line pass- 
ing over a ridge. In these cases it is only necessary to 
take into account the slope of the valleys in question, 
the positions and elevations of available passes, and the 
side slope of the ridges. 

The slope of the bed of a valley, in hilly country, 
usually forms a concave curve, the rate of slope gradu- 
ally increasing from the lower to the upper end. In a 
valley of considerable length this increase in the rate 
of slope may be very gradual or, in short valleys rising 
to a considerable height, it maybe more sudden. The 
profile ABCD in Fig. 14 shows the slope of a short 
valley which decreases in slope from about ten feet 
per hundred at the upper end to about two feet per 
hundred at the lower end. 

When a map of the country to be traversed is avail- 



LOCATION OF COUNTRY ROADS. 55 

able, showing the positions and elevations of the points 
controlling the location, the work is very much simpli- 
fied, the reconnaissance may for the most part be 
limited to a study of the map, and the routes may be 
sketched upon the map to be tried in the field. If the 
map at hand is an accurate contour map on a sufficiently 
large scale, the entire location may be worked out in 
detail upon the map, leaving only the work of staking 
out the line to be done upon the ground. 

Maps may be obtained, in most parts of this country, 
upon which the horizontal positions of points may be 
readily fixed with sufficient accuracy for the purposes 
of the preliminary examination. Where such maps are 
not obtainable, the positions of points must be ascer- 
tained and a rough map prepared. For this purpose 
directions may be measured with a pocket compass, 
and distances estimated or obtained by the use of an 
odometer or pedometer, as may be most convenient. 

Differences of elevation are easily obtained with a 
fair degree of accuracy by the use of an aneroid ba- 
rometer, and slopes may be measured with a hand 
level. 

Where the rough means ordinarily employed in the 
reconnaissance are not sufficiently accurate to deter^ 
mine the controlling points of the lines to be adopted, 
a more complete examination of the country may often 
be made by a rapid topographical survey by means of 
the transit and stadia method. 

Whatever means may be adopted for doing the 
work, the preliminary examination should determine a 
map showing the approximate positions of the con- 
trolling points through which the road must pass, and 



$6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

enable a rough sketch to be made of the slopes of the 
country through which the line is to be run. 

Art. 21. Placing the Line. 

After the preliminary examination of the locality is 
complete and the positions and elevations of the con- 
trolling points of the line are known Avith reference to 
each other, the line must be selected and run in upon 
the ground, or, if the reconnaissance is not conclusive 
as to the position of the best line, it is advisable to 
run in two or more lines and make a more detailed 
comparison between them. 

The controlling points of a line are those points at 
which the position of the road is restricted within 
narrow limits, and is not subject to change. These 
may be points where the location is governed by the 
necessity of providing for traffic, or points where the 
position of the line is restricted by topographical con- 
siderations, such as a summit over which the line is to 
pass a ridge or a favorable location for a bridge. 

Where the line is to be located to an uniform gradi- 
ent, it should be started from the controlling point at 
the end of the grade, which is usually the summit. It 
is then laid off along the slope in such manner as to 
cause it to have continuously the rate of grade decided 
upon. Taking D (Fig. 14) at the summit of the valley 
as the controlling point, it is seen that the distance 
from C to D is sufficient to give a gradient of 10 in 
TOO by following directly down the valley, and the line 
with that gradient may be run in that manner. 

The maximum gradient from A to C is, however, 
only 5 in 100, and if thought advisable the same maxi- 



58 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

mum graaient may be used between C and D by run- 
ning the line DHC diagonally down the slope, as 
shown. This line, having one half the gradient, will 
have about twice the length of the line CD. 

In running this line it is started from the highest 
point of maximum grade, and points at the surface of 
the ground are continually selected, in advance of the 
placing of the line, which are at the proper elevation 
to permit the grade to pass through them. This may 
be accomplished by setting off the angle of the gradi- 
ent upon the vertical circle of the transit, or upon a 
gradienter, and sighting upon a rod which is moved 
until the line of sight strikes it at the same height from 
the ground that the instrument is setting. The points 
for the line may also be found by running a line of 
levels ahead of the transit line (a hand level is conveni- 
ent for this purpose) and pacing distances upon which 
to reckon the gradient, the distances and elevations 
being frequently checked upon those of the measured 
line. 

The location of a gradient upon a common road 
differs from that upon a railroad only in that steeper 
gradients are used, sharper curves or angles may 
be employed, and the gradients need not be lessened 
on ordinary bends or curves. If the line is to make 
a turn upon the slope as at //", the grade should be 
flattened at the turn, and a curve of as large radius as 
possible, without too great expense for grading, be in- 
troduced. 

In a manner similar to the above a line might be 
run from D on the other side of the valley, which 
using a 5^ gradient would give the line DML, reach- 
ing the bed of the valley at the point L. A lighter 



LOCATION OF COUNTRY ROADS. $9 

gradient may be obtained from A to i? by starting 
from D and going down by a continuous gradient of 
4 in lOO on the line D F G A, and greater or less rates 
of descent may be adopted and lines corresponding to 
them located, as may be considered advisable. 

The centre-line for a final location should be care- 
fully run, and points permanently marked from which 
it may be relocated when necessary. An accurate line 
of levels should also be run over the centre-line and a 
profile drawn, upon which the grades may be estab- 
lished and earthwork estimated. 

After placing the centre-line, topography should be 
taken carefully upon each side of the line for some 
distance, and a map drawn showing the topography 
and giving elevations by means of contours. This will 
serve to show whether the line is placed to the best 
advantage, and whether any changes are desirable. 
This is especially necessary over rough ground or 
where the line is on maximum gradient, as frequently, 
and perhaps usually, the first line run will be useful 
only as a preliminary line, which with its accompany- 
ing topography will permit a proper location to be 
made. 

Art. 22. Comparison of Routes. 

In selecting a line for the construction of a road the 
principles already mentioned in the early part of this 
chapter should be had in mind. The line must be well 
designed to accommodate the traffic. It should have 
as easy grades, short length, and small rise and fall as 
is consistent with a reasonable cost of construction, in 
order to give light costs for transportation and for 
maintenance. 



6o A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Suppose in the case shown in Fig. 14 that it is desired 
to connect the village at the point A with the point D 
and with the roads leading through the passes at F 
and /. Which line it will be the most advantageous 
to adopt depends upon the relative importance of the 
traffic to the various points considered. 

The shortest, and probably cheapest, line from A 
to D would be obtained by following the valley over 
the line ABCD, which line, as shown by the profile, 
would give a maximum gradient of 10 in ico between 
C and D. The line FB joining the first line at B 
would afford communication with the summit at F 
with a maximum gradient of 5 in 100. If the traffic to 
the point D be small and unimportant, so that addi- 
tional expense in reducing the gradient from C \.o D 
is unadvisable, these lines might prove a satisfactory 
location. 

If, however, i) be a point of importance and the 
traffic from ^ to Z^ heavy, it will be necessary to adopt 
some means to reduce the gradient from C to D. 
Leaving out of consideration the point F and consider- 
ing B and C as points of minor importance, it might 
be advisable to use the line ALMD with an uniform 
5^ gradient from D to Z, and branches to connect 
with C and B. This would give a line but little longer 
than the valley line, with only one half the ruling gra- 
dient of that line. 

If C is not important and can be neglected while B 
and F must be considered, the line ABEND has a 
maximum gradient of 5 in 100, and connects A with 
the points BF and D with a minimum total length of 
road (being less than the valley line first considered). 

When B and C must both be considered as of imr 



LOCATION OF COUNTRY ROADS. 6l 

portance as well as F and D, the lines ABCHE and 
HD will give a ruling gradient of 5 in 100 to both F 
and Dy and passing through B and C with a somewhat 
longer line than in the last case. 

This arrangement would make the length of haul 
from ^ to Z^ and i% each longer than by the first line 
considered ; but the gradient to D would be lighter, and 
the total length of road to be constructed and main- 
tained would be less. 

In case the points B and C are both unimportant, 
and the line through the valley may be neglected, the 
line AGFD provides a ruling gradient of 4 in 100 from 
A to both F and D, and connects them with each 
other, with about the same length as the shortest 5^ 
gradient. When the point / must be taken into ac- 
count, this line may be connected with / by the line 
6^7 having a gradient of 4 in 100. This would give the 
shortest line of uniform gradient to connect A with the 
three points /jpand D^ and possibly a desirable line to 
construct when the line through the point / is impor- 
tant, even if the valley road from y^ to -5 is also neces- 
sary. 

The lines upon the side slopes are usually more ex- 
pensive to construct than the valley lines, and the dif- 
ferences of first cost of the various lines must of course 
be considered. The importance of a difference in ex- 
pense of construction depends upon the traffic to be 
hauled over the road and the kind of surface to be 
used. Where a broken-stone or gravel road is to be 
constructed at considerable expense, the difference of 
cost due to a change of location is relatively less im- 
portant as being a less percentage of the whole cost, 
while the difference of tractive effort due to grade is 



62 A TEXT-BOOK ON kOADS AND PAVEMENTS. 

of more importance, as being a higher percentage of 
that upon the level, than would be the case with an 
ordinary earth road. 

As is easily seen from the above the choice of a 
location for a road, while depending upon principles 
easily stated, is in reality a matter requiring the use of 
judgment, and is not readily reducible to a financial 
comparison stated in money values, because the data 
concerning the volume of the traffic and the cost of 
conducting it can be determined only very roughly, 
and contains many elements of error. For purposes of 
comparison to aid the judgment, approximate data 
may often be assumed or determined by a study of the 
localities affected. In some cases observations may be 
made of the number of teams of different classes pass- 
ing certain points within certain times, to give a basis 
for estimation of the annual volume of traffic. In 
other cases, the annual hauling traffic, which is usually 
the most important portion of the traffic in considering 
location, may be estimated from the known interests of 
the locality. Thus, if the produce of a certain section 
of farming country must be hauled over a given road 
to market, the amount of this produce may be esti- 
mated from the acreage, and the relative number of 
loads upon different grades then determined. The 
cost per load over the road would then need to be as- 
sumed in order to find the annual value of a reduction 
of grade. 

In the same manner, the effect of changes of length 
and in the amount of rise and fall may be found as 
indicated in Arts. 17 and 18. 

All of these items must be combined to find the rela- 
tive total costs of transportation for each route. The 



LOCATION OF COUNTRY ROADS. 63 

cost of construction and of maintenance for each line 
must then be estimated, and that Hne is the most ad- 
vantageous which makes the sum of the annual charges 
and the interest on the first cost a minimum. Where 
several lines of traffic are to be considered together as 
in Fig. 14, the cost of conducting all of the traffic by 
each system of lines that may be employed must be 
considered, the entire cost being made a minimum for 
the system to be adopted. 

Art. 23. Changing Existing Locations 

The problem that arises oftener than any other in 
country-road location is that of improving short 
stretches of road, where, owing to defective location, 
the grades are unnecessarily heavy, the length unneces- 
sarily great, or the ground over which the road may 
pass such as to make its maintenance in good con- 
dition difficult and expensive. The first of these is 
the most common defect of ordinary country roads, as 
shortness of distance has very commonly been obtained 
by the disregard of the desirability of light gradients, 
which in very many cases are easily obtainable. 

The principles to be observed and methods of pro- 
cedure in making the new location are exactly the 
same as in an original location, save that in this case a 
road already exists, and the question of economy is one 
of determining whether the advantages to be obtained 
in lessened cost and transportation and maintenance is 
sufficient to warrant the expense of attaining new 
right of way and constructing new road. 

In Fig. 15 is given an example that is frequently met 
in practice, where the existing road abed runs over the 



64 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

point of a hill, with heavy gradient, while a line of very 
much lighter gradient might be located around the 
base of the hill through the pass at e^ giving a greater 
length of road, but much less rise and fall. The line 
bed in the figure has a length about 800 feet greater, a 
rise and fall 70 feet less, and a maximum gradient one 
half as steep as the line bed. These relations are 
shown in the profile in Fig. 15. 

If the road in question be a common earth road, 
I foot of rise and fall may be taken as equivalent, in the 
work required to haul a load over it, to 20 feet of dis- 
tance, and the 70 feet saved by the new location would 
be equivalent to 1400 feet of distance. Hence, the 
line bed may be considered as having an equivalent 
length for purposes of traffic 1400 — 800 = 600 feet 
shorter than the line bed. In addition to this, loads 
may be taken over the new line in direction b to d 
more than double, and in direction from d to b triple, 
in weight those that can be taken by the same power 
over the old line. 

A further improvement of the line may also be 
possible, if the new line can join the old one at a point 
lower down than b^ by running a lighter gradient than 5 
in 100 from the point e. Thus the line e/a would give 
an uniform gradient of 4^, but would require the con- 
struction of more new line. 

In considering changes of location, it is also neces- 
sary to take into account the interests of adjoining 
owners. Houses and buildings are largely located with 
reference to the existing position of the roads, and 
changes in the position of a road may involve injury to 
such property. The question then becomes largely 
one of sacrificing the interests of the users of the road. 



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66 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

or those of the adjoining owners — a question that 
should be, but commonly is not, decided by consider- 
ing what will be of most advantage to the general com- 
munity. 



CHAPTER IV. 
IMPROVEMENT OF COUNTRY ROADS. 

Art. 24. Nature of Improvements. 

Ordinary country roads may be classified as earth 
roads, gravel roads, and broken-stone roads. The 
larger number of common roads throughout this coun- 
try belong of necessity to the first class. In a few of 
the more enterprising communities the more important 
roads are constructed of gravel or broken stone. 

The percentage of roads of the better class is, how- 
ever, very small and although there has recently been 
a distinct improvement in this particular, the inability 
of rural communities to at once raise the funds neces- 
sary for the general construction of first-class new 
roads will cause their increase to be very gradual. 

Improvement in country roads may be of several 
kinds 

(i) Changes in location, by which better alignment 
or better gradients may be obtained, or by which the 
natural conditions of surface or drainage may be im- 
proved. This has been discussed in Chapter III. 

(2) Reconstruction of the road-bed, as in regrading 
steep slopes to give lighter gradients, or in raising the 
road-bed across low and wet places to provide for 
drainage. 

67 



6S A TEXT-BOOK ON ROADS AND PAVEMENTS. 

(3) The construction of artificial drainage where a 
road is inclined to be wet, as already discussed in 
Chapter II. 

(4) Improvement of the surface, which may consist 
in reforming the surface of natural earth, or in the 
construction of an artificial surface or pavement, the 
latter of which will be discussed in separate chapters. 

The problem in common-road improvement is for 
the most part that of making the most of the roads 
that exist, rather than reconstructing them with new 
material. The materials and funds immediately avail- 
able must be used to secure as much improvement as 
possible. 

Earth roads, under the most favorable circumstances, 
do not usually attain any high degree of efificiency, 
and are not economical under any considerable traffic. 
They are, however, capable of much improvement, and 
if properly managed need not become, as they fre- 
quently do, practically useless during a large portion 
of the year, although they are always more difficult 
and expensive to maintain in a good condition than 
roads of a better and more permanent construction. 

Art. 25. Earthv^ork. 

Improvements to the road-bed of an existing coun- 
try road may have for their object the reduction of 
gradient upon steep inclinations, by cutting the ma- 
terial from the road-bed and lowering the surface of 
the road on the upper part of the grade, and filling in 
correspondingly on the lower part, or they may be 
intended to provide better drainage by raising the 
road across low ground. 



IMPROVEMENT OF COUNTRY ROADS. 69 

In the construction of new roads, the formation of 
tne road-bed consists in bringing the surface of the 
ground to the grade adopted for the road. This grade 
should be carefully established upon an accurate pro- 
file of the line, in such manner as to give as little 
earthwork as possible, both to render the cost of con- 
struction low, and to avoid unnecessarily marring the 
appearance of the country in vicinity of the road. 
The most desirable position of the grade line is 
usually that which make the amounts of cut and fill 
about equal to each other, especially where room for 
borrow-pits, or spoil-banks, would be expensive, and 
it is desirable to make the embankment for the most 
part of the material taken from the road excavations. 
On side-hill work, one side of the road is commonly 
in cut and the other in fill, and where the side slopes 
are steep, it is usually better to make the road mostly 
in cut on account of the difficulty of forming stable 
embankments on steep ground. 

Where embankments are to be constructed, the sur- 
fiice of the ground should be cleared of all vegetable 
matter and soft material before beginning the placing 
of the earth-filling, in order to give a firm base to the 
bank and permit it to bond with the earth below. 
The material of an embankment should be as homo- 
geneous as possible, and all perishable matter should 
be carefully excluded from it. It should be deposited 
by beginning at the outside and working toward the 
middle in such a way as to give a concave section to 
the top of the bank during construction, which tends 
to prevent sloughing off along the lines of the joints 
between the various layers. It is also best to build an 
embankment a little narrower at bottom and wider 



70 A TEXT-BOOK ON ROADS AND PAVEMENTS- 

at top than it is intended to remain, and afterward 
trim down the edges to the proper slope. 

Earth in an embankment will compact closer than 
it is found in the natural state. On an average it will 
shrink about one tenth of its bulk. The allowance to 
be made for settling in forming an embankment de- 
pends upon the method of construction. Where scrap- 
ers are used, the earth will usually be well compacted 
in placing, and no allowance is necessary ; with dump 
carts or wagons the compacting is not so thorough, 
and a small allowance should be made ; while when 
wheelbarrows are used or the earth is thrown into 
place with shovels, an allowance of lo or 12 per cent 
must be added to the height of the embankment, in 
order to allow for the final shrinkage. Rock occupies 
more space in embankment than in excavation, and 
does not need allowance for shrinkage. 

In constructing embankments across wet and un- 
stable ground, it is frequently necessary to form an arti- 
ficial foun-dation upon which to place the earth em- 
bankment. This may be accomplished in some cases 
by excavating a little of the soft material and substi- 
tuting sand or gravel, or in other cases it may be 
advisable to employ layers of brushwood or fascines 
as a support for the embankment. Sometimes it may 
be possible to drain the soft material by deep ditches 
so as to render it capable of sustaining the road, and 
in all cases drainage should be provided in so far as 
possible to make the embankment more secure. 

When embankments are to be formed on sloping 
ground, the surface of the ground should be stepped 
off, in order to hold the earth-filling from sliding upon 
the natural surface at the line of contact between the 



IMPROVEMENT OF COUNTRY ROADS. 7 1 

two, until it becomes sufficiently settled for the de- 
velopment of cohesion to cause it to become one solid 
mass. 

In many cases where roads are to be constructed 
along steep slopes, it is found cheaper to use retaining 
walls to sustain the road upon the lower side and the 
earth-cutting on the upper side than to cut long slopes 
or form high embankments. 

Catch-water drains are necessary on the natural sur- 
face above the top of all high slopes in cuttings to 
prevent the surface-water from washing down and 
destroying the face of the slope. 

Where springs are tapped by a cutting, drains must 
be provided to remove the water without injury to 
the slope ; and where the subsoil may become wet in 
rainy weather, it may be necessary to provide sub- 
surface drains along the slope to prevent the earth 
becoming saturated and sliding down into the road- 
way. 

Slopes, both of excavation and embankment, are 
greatly improved by being sodded or sown with grass. 
This aids in the maintenance of the slopes, by render- 
ing them more capable of resisting the abrading action 
of such water as falls upon them. It also greatly im- 
proves their appearance. 

The most important principle involved in the forma- 
tion of a road-bed, which should be always in mind, is 
that earth in order either to sustain a load or to main- 
tain a slope, must be kept dry, or at least prevented 
from becoming saturated with water, as both the 
cohesive and irictional resistances of earth are dimin- 
ished or destroyed when it becomes wet, and it is 
also then liable to the disturbing action of frost. 



72 a text-book on roads and pavements. 

Art. 26. Drainage. 

Drainage is especially important upon earth roads, 
because the material of the road surface is more sus- 
ceptible to the action of water, and more easily- 
destroyed by it than are the materials used in the 
construction of the better class of roads. When 
water is allowed to stand upon the road, the earth is 
softened and readily penetrated by the wheels. The 
action of frost is also apt to be more disastrous upon 
the more permeable surface of the earth road, having 
an effect to swell and heave the roadway and throw 
its surface out of shape. It may in fact be said that 
the whole problem of the improvement and mainte- 
nance of ordinary country roads is one of drainage. 

In underdraining an earth road on account of the 
permeability of the surface, provision must be made 
for carrying off the water which penetrates through 
the surface, as well as that due to natural wetness of 
the subsoil. The surface should of course be made of 
such form and material as to cause the water to flow 
off without penetrating as far as possible ; but in 
damp weather wheels will mark the surface somewhat, 
and water held in the ruts so formed will soak into the 
earth, and unless at once removed below soften it so 
that the next wheel makes a deeper rut, with the 
final result of destroying the form of the road as well 
as its power to sustain the loads that come upon it. 

The necessity for the application of artificial sub- 
drainage in any case is determined by local conditions, 
the character of the soil, and natural drainage. An 
examination of the line of the road in wet weather, 
observing whether water stands upon the ground, the 



IMPROVEMENT OF COUNTRY ROADS. ^l 

direction of flow of surface-water, and whether that 
which penetrates the ground drains away quickly is 
usually 'an efficient aid in forming an opinion as to the 
necessity for drainage. 

The methods employed in draining are considered 
in Chapter II. Dependence is most commonly placed 
upon shallow side-ditches, which are seldom of much 
value except to carry off surface-water ; and even when 
the side-ditches are deep, they can only be efficient 
for subdrainage when the soil is of a very open, 
porous nature. In other cases they will not draw the 
water from the subsoil under the middle of the road, 
and cross-drains or a centre drain should be provided. 

The common neglect of proper drainage is undoubt- 
edly very largely responsible for the general bad con- 
dition of country roads. 

Art. 27. Earth-road Surface. 

The method which should be adopted for the im- 
provement of the surface of an earth road depends 
upon the nature of the material of which it may be com- 
posed. When the material is loose sand, the surface 
will be more firm if the sand be damp and more 
unstable in dry weather. In such case a small admixt- 
ure of clay in the surface layer may ^vj^ cohesion to 
the surface when dry, or a layer of clay six or eight 
inches deep may form a hard and comparatively 
durable surface, as it is easily drained when upon the 
sand road-bed. 

Clay soils as a rule absorb quite freely the water with 
which they may be held in contact, and soften when 
saturated, but are not readily permeable, and hence are 



74 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

not easily drained from below. Used alone they are 
consequently the least desirable of road materials. 
When dry, clay may make a very hard and durable sur- 
face, and it may give good results as a covering for a road- 
bed of more pervious material, or it may form a stable 
road-bed when protected by a surface which does not 
soften so readily and prevents the surface-water from 
reaching the clay beneath. In building over clay, san j 
or gravel may frequently be mixed with the clay to 
/orm a surface layer which will be less acted upon 
by water. When rather coarse sand or small gravel is 
used for this purpose and a small proportion of clay 
just sufficient to bind the particles of sand together, 
a very hard and compact mass is formed, nearly im- 
pervious to water and but little acted upon by it. Ma- 
terial of this nature found in a natural state is known 
as hard-pan, and is very stable and durable. A layer 
of sand a few inches deep may also sometimes be 
employed to form a surface over a clay road-bed which 
will not soften in wet weather, and will afford protec- 
tion to the clay beneath. 

When other material cannot be obtained, clay roads 
are sometimes improved by burning the clay so as to 
form a more porous material for use as a surface layer. 
This method, however, is somewhat expensive, and 
other materials may usually be employed at less cost. 

Soils composed of mixtures of sand and clay or of 
gravel and clay are usually easier to deal with than clay 
itself, and commonly form the best natural roads. They 
vary in character from the light sandy loams to heavy 
soils partaking very much of the nature of clay. The 
sandy soils take up water readily and become soft when 
wet ; but they are pervious and easily drained^ and they 



IMPROVEMENT OF COUNTRY ROADS. 75 

may be compacted into a firm surface in dry weather. 
The heavier soils take up water readily and become soft 
when wet, but are less pervious and drained with more 
difficulty, though much more easily than a clay. 

The material of a road surface should always be such 
as may be compacted to a firm and hard surface. 
It should not, therefore, be formed of the soft ma- 
terial which may be washed into the gutters. The sur- 
face must be formed with a crown at the middle suffi- 
cient to shed the water which may fall upon it into the 
gutters, and prevent water from standing upon the 
road. The slope necessary to shed the water readily 
is about I in 20, and the most desirable section is usuv 
ally that composed of two planes of equal inclination, 
rounded off in the middle and sloping uniformly to the 
sides, as shown in Fig. 16. 

In the construction of an earth-road surface, road- 

Fig. 16. 

machines or road-scrapers may often be employed to 
advantage, especially when no grading is to be done 
other than giving the road the proper crown. The gut- 
ters may thus be formed, and the surface shaped up 
with comparatively little labor. 

After the material is in position, the surface should be 
compacted to the required form by rolling with as 
heavy a roller as may be available. This is a very im- 
portant matter in attempting to form a satisfactory 
earth road, and is almost indispensable to success. If 
the loose earth be thrown into the middle of the road 
to be compacted by the wheels of traffic, the action of 



^6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the wheels will be to cut it, or at least to pack it in a 
very uneven manner, producing a surface uneven and 
full of ruts, which will hold water and ultimately cause 
the destruction of the road. In case, however, the sur- 
face be properly rolled, it may usually be made suffi- 
ciently firm to hold up the wheels and retain its form 
under the traffic, and if kept free from ruts until thor- 
oughly compacted will thus be rendered much more 
capable of resisting the penetration of water and shed- 
ding it into the side gutters. 

Art. 28. Gravel Roads. 

Gravel roads may vary from that in which a thin 
coating of gravel is used as a wearing-surface upon 
an earth road to that in which gravel is used as a sur- 
face for the heavy Telford construction of a road of the 
first class. These latter constructions will be treated in 
Chapter V, under the head of " Broken-stone Roads." 

In the improvement of a country road, where the 
construction of a good Telford or Macadam road can- 
not be undertaken, a surface of gravel may frequently 
be used to advantage, giving much better results than 
could be obtained with the surface of earth. Even 
a light layer of gravel may frequently prove of very 
great benefit. 

Where the subsoil is of a porous nature and well 
drained, a layer of three or four inches of gravel, or some- 
times even less, well compacted, will constitute a very 
considerable improvement ; especially if, as is usual with 
these light soils, the nature of the material of the road- 
bed is particularly unsuitable for the wearing-surface, 
difticult to compact sufficiently to shed water, and likely 
to become soft when wet. 



IMPROVEMENT OF COUNTRY ROADS. f^J 

Where the road-bed is of clay a deeper layer of 
gravel, at least 6 inches, is usually required for effective 
work, as the gravel must be deep enough to prevent 
the weight of the traffic forcing the surface layer into 
weak places in the clay beneath, and also to effectually 
prevent the surface-water from reaching the clay. 

Gravel to be used on roads should be sharp and 
comparatively clean. In order to bind well in the road 
it should usually have a small admixture of clay. 
Gravel in which the stones are round or oval, such 
as is commonly found in the beds of streams, is unfit 
for the construction of roads ; the small stones of which 
it is composed, having no angular projections, will not 
bind together, and even when mixed with clay may turn 
freely, and will be difficult to firmly bed in position. 
Pit gravel is usually more sharp, but is frequently found 
mixed with considerable earth, which, as well as the 
larger stones should be removed by screening before 
using the gravel. Screens of if inch and f inch open- 
ings may be employed for this purpose — that material 
only which passes the larger and is rejected by the 
smaller being used in the work. 

In the construction of a road with gravel surface the 
road-bed should first be brought to the proper grade, 
with a form of cross-section the same as that to be 
given the finished road. The gravel is then placed upon 
it and rolled to a surface, or left to be compacted by 
the traffic. It is always advantageous when possible to 
compact the road by rolling. The road-bed should be 
well rolled before placing the gravel, and the gravel 
surface afterward. A smooth hard surface may thus be 
produced, upon which the wheels of loaded vehicles 
may roll without producing any visible impression. 



yS A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Where the compacting of the road is left to the traffic 
constant watchfulness is necessary to prevent unequal 
wear and the formation of ruts. 



Art. 29. Maintenance of Country Roads. 

The maintenance of a country road in good con- 
dition is a matter requiring constant care and watch- 
fulness. Any small breaks in the surface must be 
immediately repaired, and ruts filled and smoothed 
before they become serious. 

The work required to keep a road in repair depends 
upon the nature of the surface and the efficiency of 
the drainage. A well-constructed road of good ma- 
terial will be much easier and less expensive to keep in 
repair than one in which the surface is not firm enough 
to resist the cutting action of the traffic, or which has 
a surface compound of material readily softened by the 
action of water which may fall upon it. 

Earth roads under the most favorable conditions are 
expensive to maintain, and especially so under the 
common system of repairing once or twice a year, or 
at long intervals. This system is not only costly in the 
work required, which usually amounts to a practical re- 
construction of the road each time repairs are under- 
taken ; but it is ineffectual in that the road for the larger 
portion of the time is out of repair and in bad condi- 
tion, even if the work of construction has been well 
done, which is not usually the case where this method 
obtains. 

The only way to keep an earth road in good con- 
dition is by the employment of men whose business it 
shall be to continually watch the road, and make such 



IMPROVEMENT OF COUNTRY ROADS. 79 

small repairs as may be necessary from time to time. 
The small washes that may occur during heavy storms, 
ruts formed by wagons travelling in the same track, or 
in passing over soft spots when the road is wet, or 
any small breaks in the surface of the road, should be 
at once attended to and carefully filled with new 
material. 

Where small repairs are needed over a considerable 
area of the road the use of the road-machine is usually 
advantageous, as giving an easy method of smoothing 
up the surface. The use of a roller is also nearly 
always of value, both to assist in smoothing the surface 
to the proper form, and to give compactness to it. By 
the occasional use of these machines through the dry 
seasons a road may be kept crowning and hard, so that 
most of the rainfall will be quickly shed off into the 
side gutters without injury to the road. 

When there are long-continued rains, or when the ice 
and snow of winter are melting in the spring, an earth- 
road surface will necessarily be more or less softened 
and cut by passing vehicles ; and at such times a road 
of this character cannot be maintained in the same 
condition as in dry weather, or in the condition which 
would be possible with a less permeable surface, but if 
at the beginning of the wet period it be in proper form 
and if the subdrainage be efficient, the injury to the 
road as well as the duration of the bad condition, will 
be reduced to a minimum. As soon as possible after 
such a wet time, the roads should be gone over with 
the scraper and put into proper form, and then rolled 
down hard. It is advantageous to have this done be- 
fore the ground becomes thoroughly dry and hard, as 



8o A TEXT-BOOK ON ROADS AND PAVEMENTS. 

it will work more freely, and may be compacted much 
closer by the roller than afterward. 

In repairing a road where the gutter is filled with 
soft material which must be removed to afford a ire 
channel for the surface-water, this soft material shou 
not be scraped upon the middle of the road, as it w i 
not form a good wearing-surface. Where, however, 
a road is in fairly good condition, and merely needs 
a little smoothing up, it is desirable to work from the 
gutter, scraping the material lightly toward the middle 
until the proper crown is obtained. 

The difificulty and cost of maintaining a road will of 
course vary with the nature of the trafific that passes 
over it. A road for light driving will be much easier 
to keep in repair than one used by heavy loads, and 
as the amount of heavy traffic becomes greater the 
economy of the earth-road surface is lessened, and the 
desirability of the substitution of a more durable wear- 
ing-surface increases. 

The width of the wheel-tires upon which the loads 
are carried is also important in its effect upon the cost 
of keeping a road in repair. Narrow tires cut and rut 
the surface of a road, while those of sufBcient width act 
as rollers to compact the material. For the best results 
the tires should be as wide as possible, and the front 
and rear wheels of a wagon should not run in the same 
track. The lighter tractive effort required for wide 
tires on compressible road surfaces has been referred 
to in Art. 2. 

Art. 30. Width of Country Roads. 

The width of the roadway upon country roads 
should be only sufficient to provide space for the easy 



IMPROVEMENT OF COUNTRY ROADS. 8 1 

conduct of the traffic. For roads of ordinary traffic 
this requires only that there shall be room for teams 
moving in opposite directions to freely pass each 
other. An available width of i6 feet is ample for this 
purpose, and 14 feet is often sufficient. Too great 
width in the roadway causes an unnecessary increase 
in the cost of constructing and maintaining the road. 
Where the road-surface is of earth it will be much 
easier to drain it if it be narrow than if it be wide. If 
deep side-ditches be depended on for subdrainage, the 
nearer they are together the more effectively will they 
drain the subsoil under the middle of the road. Side 
ditches must, however, be far enough apart So that a 
berm may be left on each side between the travelled 
part of the road and the ditches. Thus In Fig. 7, p. 31, if 
the macadamized portion represents the travelled part 
of the road, the berm between that portion and the 
ditches could be sown with grass and show the line of 
the road as a guide to travel. 

When covered drains are used for subdrainage the 
gutters at the side may be made shallow and placed 
next the travelled part of the road, giving much less 
surface to maintain and greater efficiency to the drain- 
age than in a wider road. Such sections are shown 
for earth roads in Figs. 6 and 16. Fig. 4 shows a 
similar construction with side-drains under the gutter 
and a broken-stone surface. Fig. 17 shows the 
ordinary form of a country road with broken-stone 
surface. On important roads the paved portion is 
commonly 16 or 18 feet in width, but on roads of 
lesser importance it may be less, and under light traffic 
a width of 10 feet maybe sufficient — teams, when neces- 
sary, turning out upon the sod to pass. Where a less 



82 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

pervious covering is employed, as with gravel or broken 
stone, width will not have the same tendency to render 
drainage ineffectual as in the case of an earth road, 
because comparatively little water will pass through 
the road-surface to the subsoil. The cost of main- 



Fig. 17. 



irrf/, 



tenance may not, therefore, be so materially affected 
by the width, although the cost of construction, and 
hence the length of road, that may be built for a give 
sum will be directly dependent upon it. 

While the improved portion of the road should be 
as small as is consistent with the proper discharge of 
the duty required of it, the available right of way need 
not be so restricted, but should be laid out wide 
enough to permit of the widening of the used portion 
when necessary, and allow room at the sides for pedes- 
trians, with a grass border and line of trees. When 
trees are planted along the roadway they should not 
be placed so as to form a dense shade over any portion 
of the travelled road, although a moderate shade is 
not a disadvantage, and care should be used that they 
are not near enough to a covered drain to permit the 
roots to grow into the drain and choke it. 

Art. 31. Economic Value of Road Improvement. 

The value of a road improvement to a community 
and the amount of money that may reasonably and 
profitably be expended in the construction and main- 
tenance of common roads is a subject the discussion of 



IMPROVEMENT OF COUNTRY ROADS. 83 

which leads different persons to widely different con- 
clusions, depending upon the point of view and the 
data assumed. 

The economic principles involved in a choice of 
location have already been discussed in Chapter III ; 
and the general value of any other improvement, in so 
far as it relates to the economic conduct of the traffic, 
may be considered in the same manner. Any improve- 
ment, either in position or surface, that has the effect 
of increasing the loads that may be taken over a road 
by a given power lessens the number of loads neces- 
sary to carry the traffic, and effects a saving in time 
and labor of men and teams, which may reasonably be 
considered to have the same money value as the time 
used in the work. 

On ordinary country roads in dry weather, the amount 
of load that can be hauled is usually determined rather 
by the grades than by the nature of the surface. Un- 
less the gradients are very light the amount of load 
that can be carried on a broken-stone surface does not 
differ greatly from what may be taken on a dry and 
hard earth road. In improving a road by substituting 
a hard surface for a surface of earth the gradients and 
location should therefore always be carefully studied, 
with a view to deriving the full practical benefit from 
the hard surface in the light traction that it may re- 
quire with easy ruling gradients. 

It is in wet and muddy weather that improved sur- 
faces have their chief advantage over earth roads, and 
the main object of introducing hard and impermeable 
surfaces is to eliminate the period when ordinary earth 
roads are apt to be muddy and practicall}' useless for 
the purposes of transportation, and to substitute a 



84 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

road that may be used at any season. Systematic 
drainage has a similar object. To a farming com- 
munity the economic advantage of a road uniformly 
good at all seasons is greater than might appear at 
first glance. It may in many instances amount prac- 
tically to a saving equal to nearly the entire cost of 
hauling, by permitting the work to be done at times 
when other work is impossible, thus making men and 
teams available for other duty in good weather. The 
ability to use a road at any season is also of advantage 
in the independence of weather that will make it pos- 
sible to take advantage of the condition of the markets 
in the disposal of produce or purchase of supplies. 

The nature of the roads has likewise an important 
effect upon the social life of the people in a rural dis- 
trict, and has much to do with the desirability of a 
locality as a place of residence. These items all have 
a real importance, which, while difficult to estimate in 
money values, show at once in the fact that prices of 
country property are largely affected by them. 

The nature of the country roads affect the towns to 
which the country is tributary as well as the country 
itself. They directly affect trade in seasons of bad 
weather, both in regulating the demand for supplies 
for country consumption and in controlling the supply 
of produce which is available for market ; indirectly 
also the prosperity of a rural district means that of its 
trade centre. 

All of these points must be considered in any at- 
tempt to arrive at any proper conception of the advan- 
tages of a proposed improvement. In any particular 
case the local interests will determine the relative im- 
portance of the various elements, and a careful analysis 



IMPROVEMENT OF COUNTRY ROADS. 85 

of the trade that does pass over the road and that 
would pass over it under different conditions will 
enable a judgment to be formed as to the value of 
improvements. 

The money spent in road improvement is to be con- 
sidered as an investment, which will return annual 
interest to the community in reduced costs of trans- 
portation and greater freedom of traffic and travel. 

Art. 32. Systems of Road Management. 

Several different systems for managing the work of 
constructing and repairing country roads have been 
proposed or are in use in various places. These sys- 
tems differ in the placing of the control of the roads 
and in the methods adopted for providing funds. 

The control of the roads under the various systems 
may be vested in the national government, in the vari- 
ous State governments, in county or parish organiza- 
tions or in townships or districts. In regard to the 
location of control and responsibility, it may be re- 
marked that there are two points to be kept in view. 

1st. In order that the work may be economically 
conducted, the section of country included under one 
control should be sufficient to warrant the permanent 
employment of a man', or corps of men, whose business 
it shall be to continually look after the roads, study 
their needs, and systematically conduct their improve- 
ment. It should admit of the ownership and use of 
labor-saving machinery for the economical execution 
of the work, but should not be large enough to require 
an elaborate and complicated organization. 

2d. The control of road work should be so arranged 
that, as nearly as possible, all of the interests directly 



S6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

affected by the condition of any road shall have a 
voice in its management and contribute to its support. 

Common roads are essentially local in their character 
and are not usually employed as lines of continuous 
transportation over any considerable distance. They 
are not, therefore, of State or national importance as 
lines of communication, although as factors in the 
general welfare of the people they must, of course, like 
all other such factors, be of general interest and con- 
cern to both State and nation. 

The nation, and in most cases in this country the 
State, is too large an unit to assume direct control of 
road work. In general, the interests over so large an 
area are so varied, and the requirements so different, 
as to prevent a harmonious and successful organization 
of such work with a probability of economical adminis- 
tration. In some cases, however, such control might 
be wise and proper, and the recognition of the impor- 
tance of road improvement to the general welfare of 
the State, through the payment by the State of a 
portion of the cost of permanent improvements, has in 
some instances proved a powerful stimulus to local 
action. 

The control of road management by towns and small 
districts is nearly always inefficient because the organ- 
ization is too small to support a proper management 
or provide the necessary appliances for economic work. 
Under this system the man in charge of the roads is 
usually engaged in other work, he is not a road engineer, 
and can, and is expected to, give but little attention to 
the road work. This system of control is also usually 
unfair, except in case of roads intended for the accom- 
modation of the local district only. For instance, a 



IMPROVEMENT OF COUNTRY ROADS. 8/ 

road passing through a town may be a thoroughfare 
for the towns upon each side. The principal traffic 
may be this through-trade to points beyond the Hmits 
of the town in which the road is situated. The cost of 
keeping up this road is largely due to outside traffic, 
and the intermediate town should not be required to 
bear all the expense of maintenance. On the other 
hand, the interests of the towns whose trade passes 
over the road are largely affected by its nature, and 
the people of these towns should be permitted a voice 
in determining the character of the road. Most of the 
more important roads of every vicinity pass thus 
through several towns, and the system of improvement 
by small districts works injustice both ways — upon 
those who are obliged to keep a road for the use of 
others and upon those who are obliged to use a road 
they cannot cause to be kept in proper condition. 

County management seems more successful in this 
country than any other, as a county, or two counties 
combined if necessary, is usually strong enough to 
secure intelligent management and homogeneous 
enough to have common interests. 

The proper management of the common roads in 
any community requires both experience and intelli- 
gence. A man to be efficient in such work must be 
able to make or modify location where necessary, 
judge of the value of various materials for purposes of 
construction, determine the necessity for and means to 
be adopted for drainage, and possess the executive 
ability to manage men and control scattered work. 
The work in each locality is a problem by itself, to be 
solved by careful study of the requirements of the 
community, taking into account the local natural coii'. 
ditions and available: materials and means. 



CHAPTER V. 
3ROKEN-STONE ROADS. 

Art. 33. Definition. 

BrokeN-STONE roads consist essentially of a mass of 
angular fragments of rock deposited, usually in layers, 
upon the road-bed or a foundation prepared for it, and 
then consolidated to a smooth and uniform surface by 
means of a roller or by the action of the traffic which 
passes over it. 

There are two commonly recognized systems of con- 
structing broken-stone roads, differing in the nature of 
the foundation employed, and known respectively by 
the names of the men who first introduced them into 
English practice as Telford roads and Macadam roads. 

Each of these bystems has been greatly modified in 
use since the time of its founder, and each name is now 
used to cover a general class of constructions differing 
very materially within itself as applied in the practice 
of different engineers. Each of the systems also has 
its earnest advocates, who contend for its exclusive use, 
and numerous controversies have been the result, at 
the conclusion of which each party is "■ of the same 
opinion still." The view taken by different road- 
builders in this matter, it may be remarked, appears to 
be the result usually of the local necessities of the 
vicinities in which they work, and of the skill with which 

ss 



BROKEN-STONE ROADS. 89 

the different systems have been applied in work which 
has come under their observations. In road-building, 
as in any other class of engineering works, no rigid 
rules can be laid down for universal application ; each 
road must be designed for the place it is to occupy and 
the work it is to do. 

In some parts of this country natural gravel is sub- 
stituted for broken stone in the construction of these 
roads, the methods of construction being the same as 
in using broken stone. 

Art. 34. Macadam Roads. 

Macadam roads as commonly constructed consist of 
two or more layers of broken stone, each layer being 
rolled to a firm bearing before placing the next. The 
broken stone is usually placed directly upon the earth 
road-bed. 

In constructing a macadamized roadway, the road- 
bed is first brought to the proper grade in the usual 
manner, and rolled to a uniform surface. The surface 
of the road-bed is either flat or raised at the middle to 
the same section as is to be given the finished road- 
surface. The inclined form is usually employed, and 
seems preferable on account of affording better drain- 
age in case any water finds its way through the surface 
layer. 

On village streets where curb and sidewalks are em- 
ployed, this section of the road-bed may extend to the 
curbing (as shown in Fig. 5), but on country roads a 
bench of earth should be left at the side between the 
broken stone and the gutter in order to confine the 
broken stone while it is being compacted, and prevent 



90 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

the spread of the surface materials. The form of the 
road-bed before placing the stone would then be as 
shown in Fig. i8, where the completed road is to be of 
the form given in Figs. 4 and 7. Where the road-bed 
is in embankment, it is common to construct the earth 
embankment to the height of the finished surface,, and 
afterwards excavate the material necessary to admit of 

Fig. 18. 

placing the surface layers. The embankment should 
be allowed to settle and become thoroughly compacted 
before the broken stone is placed upon it, and it is 
desirable with new embankments that they be used for 
a short time by the traffic upon the earth surface be- • 
fore finishing the road ; where, however, the material 
is well compacted in construction and can be thor- 
oughly rolled this is not necessary. 

In constructing the road-bed its proper drainage 
must be considered, and where necessary to prevent its 
becoming wet under the broken stone some means 
should be adopted to artificially drain it. 

Upon the completion of the road-bed, a layer of 
broken stone, usually from 3 to 5 inches in thickness, is 
placed upon it and thoroughly rolled. Upon this a 
second layer is placed and likewise rolled to an uniform 
surface. Sometimes a third layer is added, or in case 
of a very thin road it may consist of a single layer, the 
number of layers depending upon the thickness of the 
road. When no roller is used, the stone is usually 
spread on the surface of the road-bed to the full thick- 



BROKEN-STONE ROADS. Qt 

ness desired for the road, and left to the action of the 
traffic. 

The upper layer constitutes the wearing surface of 
the road, and upon this it is usually necessary to place 
a thin layer of finer material called binding materialy 
which may consist of rock chips, sand, small gravel, or 
sometimes loam, and is washed and rolled into the inter- 
stices of the rock, with the object of forming a com- 
pact and impervious surface. Binding material is in 
like manner often added to the lower layers of the 
road, although this has not been common practice. 
The object should be to fill the voids in the rock as 
completely as possible, serving to make the road one 
solid mass, to bind the rock more firmly together, and 
to prevent the percolation of water through the surface. 

When a road is to be constructed over a heavy soil 
not easily drained and apt to be wet and soft, a foun- 
dation consisting of a thin layer of sand or gravel may 
frequently be employed to advantage. This founda- 
tion layer will serve to prevent the stones of the lower 
stratum of macadam from being forced downward into 
the soft material of the road-bed, or the material of the 
road-bed from forcing upward into the interstices of 
the broken stone. This foundation may consist of a 
layer of sand or gravel from 2 to 5 inches thick, and 
should be well compacted by rolling before the placing 
of the broken stone. 

Art. 35. Telford Foundations. 

The distinguishing feature of a Telford road is its 
paved foundation. It consists essentially of a pave- 
ment of stone blocks set upon the road-bed and cov- 
ered with one or more layers of broken stone. 



92 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In forming a Telford road the road-bed is con- 
structed in the same manner as for macadam, being 
made either level or crowned. A pavement is then 
placed upon the road-bed from 5 to 8 inches thick, de- 
pending upon the thickness to be given the road 
material, the general practice being to make the pave- 
ment about two thirds of the total thickness of the 
road. The stones used for the pavement may vary 
from 2 to 4 inches in thickness and 8 to 12 inches in 
length ; they are set upon their widest edges and with 
their greatest lengths across the road. The irregulari- 
ties of the upper part of the pavement are then broken 
off with a hammer, and all the interstices filled with 
stone chips and wedged with a light hammer so as to 
form a completed pavement of about the thickness re- 
quired. 

Upon this pavement the layers of broken stone are 
placed, and the road-surface completed in the same 
manner as for a Macadam road. 

The practice of Telford was to grade the road-bed 
flat, and then construct his pavement deeper in the 
middle than at the sides, using for a roadway 16 feet 
wide stones about 8 inches deep at the middle and 5 
inches at the sides. This practice is still followed by 
some engineers, but it is now more common and usually 
considered preferable to make the surface, of the road- 
bed parallel to the finished surface and the pavement 
of uniform thickness. Fig. 19 shows a section of Tel- 
ford road as now commonly constructed. 

Some engineers in constructing Telford foundations 
do not roll the road-bed, but simply bring it to grade, 
and then lay the pavement by bedding the stones in 
the surface of the road-bed sufficiently to bring their 



BROKEN-STONE ROADS. 93 

tops to the proper height, in which case it is unneces- 
sary to trim off the tops with the hammer as in the 
common practice. 

An objection sometimes urged against the Telford 
foundation is that if the foundation be of hard stone it 
will cause the material above to be crushed by the loads 
which come upon it, and that greater durability in the 
wear of the road metal will be obtained by having a 




Fig. 19. 

more yielding foundation. The durability of the Tel- 
ford road has, however, been established by long-con- 
tinued usage. There is no apparent reason why a firm 
foundation should cause greater wear at the sui'face, 
and the materials below the surface are never crushed 
in the destruction of any broken-stone road. 

The relative value of the two systems must always 
be determined by the local conditions under which a 
road is to be constructed and the necessity for such a 
foundation in the particular case. 

Art. 36. Choice of Foundation. 

The proper foundation to be used for a broken-stone 
road depends upon the nature and condition of the 
road-bed upon which it is to be constructed and the 
nature of the traffic to pass over it. If a firm, well- 
compacted, and thoroughly drained road-bed may be 
obtained, of material which will not readily soften 



94 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

under the action of moisture, there will usually be no 
need for a special foundation, but the first layer of the 
macadam may be placed directly upon the surface of 
the road-bed. If, however, the road-bed is of a ma- 
terial retentive of moisture, not thoroughly drained, 
and likely to become soft in wet weather, and the 
broken stone be laid immediately in contact with it, 
the stones of the lower layer of macadam may be grad- 
ually worked down by the weight of the trafific into the 
soft earth, and the soil at the same time work up into 
the voids in the stone, causing a gradual disintegration 
of the road. It may thus also become retentive of 
moisture and subject to the disrupting action of frost. 
In this case some foundation must be provided which 
is capable of resisting the penetrating action of the soft 
material of the road-bed, and of distributing the load 
over it. This may be the Telford foundation as de- 
scribed in Art. 35, the sand or gravel foundation men- 
tioned in Art. 34, or the Telford foundation upon a 
layer of sand or gravel, depending upon the extent of 
the difificulty to be met. 

It is not intended in the above to imply that the use 
of a foundation of this character should take the place 
of proper drainage. The advisability of artificial 
drainage should always be carefully considered, and 
where the road is threatened by water which may be 
removed by the construction of drains they should be 
used, but frequently thorough drainage is difficult or 
doubtful, and it is desirable to adopt heavy construc- 
tion such as the Telford foundation gives. 

IT) some instances it may be possible, by drains under 
the road and substituting porous material immediately 
under the broken stone, to use light macadam super- 



BROKEN-STONE ROADS. 



95 



structure and do away with the necessity for the Tel- 
ford pavement in difficult soils. Thus in Fig. 20 a con- 
struction is shown applicable to wet and unstable soils, 
the space over the centre-drain and under the middle 
of the macadam being filled with large rounded stones, 
which secure drainage and form a stable bed for the 
broken stone. 

It is commonly claimed by the advocates of the 
Macadam system of construction that on any well- 
drained and well-compacted road-bed there will be no 
tendency on the part of the stone to work down or of 




Fig. 20. 



the soil to work up, and hence that the Telford foun- 
dation is an unnecessary expense. The difficulty of 
procuring a perfectly stable and reliable road-bed in 
many localities is, however, very generally recognized, 
and Telford pavements are largely used. 

It would undoubtedly be an advantage in the con- 
struction of any broken-stone road, either Macadam or 
Telford, to have a layer of sand or gravel between the 
road-bed and the pavement, both as assisting drainage 
and as providing against unequal settling of the foun- 
dation of the road. The application of it, however, 
must in any case depend upon its cost and its apparent 
necessity. In cases where drainage is difficult and the 



96 A TEXT-BOOK ON ROADS AND MVEMENTS. 

soils inclined to be damp and soft, it may frequently 
prove the simplest solution of the problem. 

Concrete foundations are often recommended for 
broken-stone roads, and would undoubtedly be very 
beneficial in most cases, but usually where so expensive 
a foundation may be employed a better surface might 
advantageously be used than broken stone. It may 
sometimes occur, however, that, in places where the 
foundation is difficult to maintain, a light bed of con- 
crete may prove of great benefit, as forming a firm and 
impervious base to rest upon damp and unstable soils. 

Art. 37. Materials Employed. 

A stone to be durable in the surface of a road should 
be as hard and tough as possible. The qualities of 
toughness and resistance to abrasion are of more im- 
portance than hardness and resistance to crushing. A 
stone may be hard and brittle, and quickly pound to 
pieces in a road surface, or it may have a high crushing 
strength and grind away quickly under abrasion, as is 
the case with some varieties of sandstone. If, how- 
ever, it be too soft, it may crush under the loads com- 
ing upon it, and thus lack in durability. 

A stone for a road-surface must also resist well the 
disintegrating influences of the atmosphere. It should 
be as little absorptive of moisture as possible in order 
that it may not be Hable to injury from the action of 
frost. Many limestones are objectionable on this ac- 
count. 

Basalt and syenite are, in general, the best materials 
for this purpose. The harder limestones in some lo- 
calities make a good and durable surface. Soft lime- 



BROKEN-STONE ROADS. 97 

stones crush under the action of the wheels, and soon 
become dust and mud. Sandstones as a general thing 
are not fit for this use. 

The material of a road surface should also be uni- 
form in quality; otherwise the wear of the surface will 
not be even, and depressions will appear where the 
softer material has been placed. 

As the under parts of the road are not subject to the 
wear of the traffic, and have only the weight of the 
loads to sustain, it is evidently not important that the 
foundation or lower layers be of so hard or tough a 
material as the surface ; and hence it is frequently pos- 
sible, by using an inferior stone for that portion of the 
work, to greatly reduce the cost of construction. 

A judgment as to the value of any given stone for 
road use can ordinarily be formed from what may be 
known of its behavior under other uses to which it may 
have been subjected, or from its appearance where it 
has long been exposed to the weather, together with 
such physical tests as may be necessary to determine if 
it possesses the special properties desired. 

Tests may be made of the power of absorption by 
drying a sample, weighing it, then placing it in water 
and reweighing occasionally until it ceases to gain in 
weight. The absorption may then be expressed as a 
percentage of the dry weight. The resistance to abra- 
sion may be found either by grinding a sample upon a 
polishing-disk, or by rattling blocks of the material in 
an abrasion-cylinder with pieces of iron, and noting 
the loss of weight in each case, and comparing such 
losses with those of a stone of known value under like 
conditions. These examinations with tests of the 
crushing strength of the material will enable an ap- 



98 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

proximate idea to be formed as to the probable wear- 
ing qualities of the stone. 

The best test of enduring properties will always be a 
knowledge of the stone as used for any purpose where 
it undergoes exposure. 

The selection of a stone for road construction will of 
course always depend largely upon what is to be ob- 
tained in the locality of the work. The importance of 
a thoroughly good material in the road surface is, how- 
ever, so great in its effect upon the durability and cost 
of repairs of the road that it may frequently be found 
economical, on roads subjected to a considerable traffic, 
to bring a good material a considerable distance rather 
than to use an inferior one from the immediate vicinity. 
It may also be suggested in this connection that in 
many instances railway transportation over a consider- 
able distance may be small compared with wagon 
transportation over a short distance, and the impor- 
tation of good material may add but slightly to the 
aggregate cost of the work. 

The size to which stone should be broken for road 
material depends to some extent upon the nature of 
the material. The harder and tougher it is the smaller 
the pieces may be without danger of crushing or shat- 
tering under the loads and shocks received in the road 
surface, and the smaller also they will need to be in 
order to be thoroughly compacted in the road. 

It is a general custom to use larger stones in the 
bottom courses of a road than at the top. A rule very 
commonly given is that the stones for the lower layers 
should be at least 2 inches in their greatest diameter, 
and not more than 3 inches, and that for the surface 



BROKEN-STONE ROADS. 99 

iayer the stones shall not be greater than 2 inches 
in greatest dimension. 

If of very hard rock the surface layer may have ij 
inches as an upper limit of size. 

The size of the rock in the lower layers does not 
seem of so great importance as that for the surface 
layers, as it is not directly subject to the weight or the 
abrading action of the concentrated wheel-loads, and it 
is probable that in some cases unnecessary expense is 
incurred in following the refinements of rigid specifica- 
tions in this particular. 

There is a difference of opinion also among road- 
builders as to the advisability of using stone of uniform 
size. Some insist quite strenuously upon this point, 
and carefully screen their stone with the object of get- 
ting it as uniform as possible ; while others declare that 
the variation of size is an advantage, and even that the 
stone should not be screened after coming from the 
crusher, except to remove the stone above the limiting 
size and when necessary to get rid of foreign matter 
in case it should contain clay or earth. 

Uniformity of size probably makes the wear more 
even, but the presence of smaller fragments facilitate 
the binding together of the material. The best prac- 
tice seems to favor the exclusion of the fine material 
from the stone, without insisting on too great uniform- 
ity in size (stones being allowed probably from J inch 
to ij or 2 inches in dimension), and then adding small 
material after the placing of the stone upon the road 
to assist binding. 

This eliminates the danger of having portions of the 
road composed entirely of fine material. 

Road stone may be broken by hand or machine, 
L.ofC. 



lOO A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Hand-broken stone is usually preferred as cleaner and 
better in shape for compacting in the road. In England 
hand-breaking is largely practised, and it is frequently 
asserted that machine-breaking injures the stone by 
crushing it in the jaws of the machine with the effect 
of decreasing its durability in the road surface. 

In American practice machine-breaking is almost 
exclusively used. It gives satisfactory results, both as 
to binding and durability, and has the advantage of 
greatly lessening the cost of construction. 

Gravel is frequently used for roads constructed in 
the same manner as with broken stone, both with and 
without the Telford foundation. The requirements of 
a good gravel for this purpose are the same as for a 
good stone. The stones of the gravel should be sharp 
and angular, and must possess the qualities of hardness 
and toughness. Water-worn material is therefore ob- 
jectionable, as it will not compact without the use of 
large amounts of soft binding material. In many places 
a hard flint gravel occurs which is not inferior to the 
best broken stone. 

Gravel not fit for surface material has sometimes been 
used to advantage under a surface layer of hard rock, 
and in some cases a surface of flint gravel has been 
used upon bottom layers of soft rock. 

Gravel should be screened to remove the larger 
stones and the fine material, and then treated in the 
same manner as broken stone. 

Blast-furnace slag may also in some localities be used 
as a road material with good results. Slag varies 
greatly in its properties, some being porous and brittle, 
other hard and tough. The ordinary slag is usually a 
good material for foundation and lower layers of the 



BROKEN-STONE ROADS. lOI 

road ; and where a good, tough slag can be obtained it 
may also be used for the surface. In some places slag 
is toughened for such use by being cooled slowly under 
a cover of ashes or cinders and afterward broken like 
rock. 

Ashes or cinders may also sometimes be employed 
as a foundation for a thin-broken stone road. They 
serve to secure good drainage and become very com- 
pact. In many cases a considerable improvement 
might be made in village streets by substituting a layer 
of ashes for an earth-road surface, and later a stone 
surface could be applied directly to the road so 
formed. 

Art. 38. Binding Material. 

It was the practice of McAdam to require that all 
the stone used upon his roads should be as nearly as 
possible of a uniform size, and that no foreign sub- 
stance be mixed with it. In more recent practice it 
has been found advantageous to use a certain amount 
of finer material to fill the interstices between the 
stones, and thus aid in the compacting of the road as 
well as render it less pervious. 

There is considerable difference of opinion upon this 
point among road-builders. A few still advocate the 
system of McAdam. Others place a thin layer of 
binding material upon the surface of the road and 
work it into the surface voids, while still others dis- 
tribute the binding material through the entire mass of 
stone composing the road. 

It is agreed that an impervious surface cannot be 
formed of blocks of hard broken stone without the ad- 
dition of gome small material to fill the voids. It has 



I02 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

also been found that when the rock is hard, such as is 
needed for good wear in a road surface, it will compact 
with difficulty, and that a certain amount of binding 
material is necessary in order that the road may be 
brought to a surface. 

The stone forming the body of the road should be 
placed and partially compacted before the addition of 
the small material, which may then be worked into the 
spaces between them. 

The office of the binding material is to hold the 
stones in place and form a bearing for them, as well as 
to prevent the passage of water between them. It has 
no duty to perform in sustaining the loads. This is 
the objection to having the binding material mixed 
with the stones in advance, as would be the case when 
unscreened stone is used. A portion of the road stones 
would be replaced by small material instead of having 
this material only in such voids as necessarily exist be- 
tween the stones. 

The quantity of binding to be used is that which 
will be barely sufficient to fill all the voids in the larger 
material. It has been contended that the lower por- 
tion of the road should be porous in order to facilitate 
the escape of any water that may find its way through 
the surface, but the tendency of the best modern prac- 
tice is in the direction of filling all the voids as nearly 
as possible, thus making the entire road practically one 
solid body and it is now commonly agreed that the sur- 
face of a properly constructed broken-stone road is very 
nearly impervious to water. 

The voids in loose broken stone comprise about 40 
to 50 per cent of the volume. In the stone when 
compacted in the road the voids are somewhat reduced, 



BROKEN-STONE ROADS. IO3 

probably ranging from 301040 per cent of the volume. 
The voids may be approximately determined in any 
case by filling a measure with the stone, shaken down 
as closely as possible, and then measuring the quantity 
of sand that can be added in the same manner. 

Binding material may consist of the screenings from 
the broken stone used in the road, of sand or small 
gravel, or of loam. To produce the best results in 
wear the material used for binding should be of equal 
hardness with the road stone. Sand, or sand mixed 
with screenings, often gives satisfactory results, and 
is more easily compacted than screenings alone. With 
the use of loam it is much easier to compact the road 
to a satisfactory surface than with harder material, es- 
pecially if the roller used be a light one. Loam has 
been used in some instances with satisfactory results, 
but the wisdom of its use is questioned by most 
authorities. 

Art. 39. Compacting THE Road. 

The materials may be compected in a road either by 
placing them in position and allowing the trafific to 
pass over them or by rolling with a steam or horse 
roller. 

The first method by itself is seldom practised when 
it is possible to avoid it. It is hard upon the trafific, 
takes a long time to reduce the road to a compact con- 
dition, and a smooth surface is with difficulty pro- 
duced. Where heavy horse-rollers are employed they 
are clumsy and inconvenient to handle, and the work 
of rolling is slow as compared with the steam-roller. 
In many instances, however, good results are obtained 



I04 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

with them. They are not so expensive in first cost as 
steam-rollers, and have not the disadvantage of fright- 
ening horses. 

Some road-builders prefer light-horse rollers of two 
or three tons weight, using them either by themselves 
or in connection with the travel. In the latter case the 
roller simply smooths off the surface as the traffic does 
the compacting. (See paper by James Owens, in Trans- 
actions American Society of Civil Engineers, Dec. 
1892.) These rollers are said to work satisfactorily 
where soft binding material is used, although longer 
time is necessary than with heavier ones. 

Horse-rollers are usually arranged so that the direc- 
tion of motion may be reversed without turning the 
roller itself around, and also so that the weight may be 
changed by placing additional weight inside the roller 
or removing it. 

Steam rollers weighing from 8 to 15 tons are most 
commonly employed for compacting the road materi- 
als. They have the advantage of forcing the materials 
at once into a firm and compact mass and producing a 
smooth surface for the immediate use of travel. They 
admit also of the use of hard materials for binding. 

In constructing a road with the use of a steam-roller, 
the road-stone is first put on to the required thickness 
and the roller passed over it to settle the stones into 
place and reduce the voids as much as possible. The 
binding material, representing a volume about equal to 
the voids in the stone, is then added, sprinkled, and 
rolled until the small material is washed and forced into 
the interstices, giving a smooth, hard surface. This is 
repeated for each layer of stone, or in some cases the 
small material is only applied to the top layer. 



BROKEN-STONE ROADS. IO5 

A thin coating of the binding material is then spread 
upon the surface and the road thrown open for travel. 

Art. 40. Thickness of Road-covering. 

The thickness nessary for a road-covering depends 
upon the amount of the traffic it is to bear and upon the 
nature of the foundation afforded by the road-bed. 
Under a heavy traffic it is advisable to make the road 
covering heavier than might be allowable for lighter 
traffic, in order to provide for wear and lessen cost of 
renewals. 

When the road-bed is firm, well drained, and not 
likely to soften at a wet season, it will always afford a 
firm bearing, upon which the covering may rest. The 
loads coming upon the road are then simply transmitted 
through the covering to the road-bed beneath, and 
there is no tendency on the part of the loads to break 
through the covering other than by direct crushing of 
its material. If, however, the road-bed may become 
soft in wet weather, it will then lose its power to firmly 
sustain the covering at all points, and ihe covering 
must possess sufficient strength to bridge over places 
where it is not supported from beneath, or a load com- 
ing upon it may break through by bending it down- 
ward at such point. The thickness of road covering, 
therefore, must be greater where the road-bed is less 
perfect. 

The intensity of freezing that may be expected also 
has an influence upon the necessary thickness of the 
road-covering. The effect of frost upon the road will 
depend in large measure upon the condition of the 
road-bed, and thus make the thickness depend in still 
greater nieasure upon its nature. Freezing will not 



I06 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

injure a dry road-bed, but if it be damp and have but 
a thin covering the road is likely to blow or be thrown 
up by the action of frost. 

For roads on considerable grades the thickness of the 
road-covering is often reduced below what is used on 
flat ones, because of the better drainage afforded by 
the slopes. It is to be remarked, however, that if the 
slopes are very steep the wear of the surface becomes 
so great, due to the horses* efforts to obtain foothold 
and to the washing of surface-waters during rains, that 
the thickness of the coating should be increased. 

Macadam roads are commonly made from 4 to 12 
inches thick, and Telford roads from 8 to 12 inches, of 
which 5 to 8 inches may be foundation pavement. 

A covering 8 to 10 inches thick is usually considered 
ample for nearly any case of a country road, unless 
laid upon bad foundation. In case of a slope of more 
than 3 or 4 degrees this may perhaps be reduced to 6 
inches, or with an especially good road-bed and good 
drainage it may even be made 4 inches. 

A thin road to be effective must have its interstices 
well filled with binding material and be thoroughly 
compacted by rolling. It will then present no voids to 
be filled by the soil pressing upward from below, and 
at the 3ame time it will be practically impervious and 
prevent surface-water from reaching the road-bed, thus 
keeping the material in good condition to sustain the 
loads. The 4-inch roads of Bridgeport, Conn., which 
are often cited as examples of successful work, are con- 
structed in this manner of exceptionally good mate- 
rial. In other cases where thin roads have proved fail- 
ures the trouble may often be traced to dampness in 
the subsoil or to lack of thorough construction. 



BROKEN-STONE ROADS. I07 

In many cases the problem to decide, in determining 
the thickness of a covering, is whether to use heavy 
construction or thorough drainage. It is easier to get 
good results with thick road-coverings, and they are in 
general safer to use; but skilful adaptation of less ma- 
terial may often save expense in construction with good 
results. The peculiar conditions of each case must de- 
cide what is best for that case. 

Art. 41. Cross-Section. 

The side-slopes necessary to enable the water which 
falls upon a broken-stone surface to drain off readily to 
the gutters is about I in 30 ; hence a crown should be 
given the road that will permit that slope. In con- 
struction the crown should be made an inch or two 
inches, depending upon the width and thickness of the 
road, higher than it is intended to remain, in order to 
allow for settlement and wear under the trafific. 

The arrangement of a cross-section has been referred 
to in Art. 30, and sections are shown in Figs. 4, 5, 7, 17, 
and 20. In some cases on country roads only the 
middle portion of the road is surfaced with broken 
stone, and a roadway of earth is left on each side, be- 
tween the broken stone and the ditches, upon which 
teams may drive in dry weather. Such a roadway 
would commonly be preferred by teams when the earth 
is dry and hard, but it renders the road more expensive 
to maintain. 

Art. 42. Maintenance of Broken-stone Roads. 

To maintain a broken-stone road in good condition 
it is necessary first of all that it be frequently cleaned 



I08 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of mud and dust, and that the gutters and surface 
drains be kept open to insure the prompt discharge of 
all water that may come upon the surface of the road. 

The best method of making repairs that may become 
necessary to the road-surface depends upon the char- 
acter of the material composing the surface and the 
weight of the traffic passing over it. 

If the road metal be of soft material which wears 
easily, it will require constant supervision and small re- 
pairs whenever a rut or depression may appear. Ma- 
terial of this kind binds readily with new material that 
may be added, and may in this manner frequently be 
kept in good condition without great difficulty, while if 
not attended to at once when wear begins to show it 
will very rapidly increase, to the great detriment of the 
road. In making repairs by this method, the material 
is commonly placed a little at a time and compacted by 
the traffic. The material used for this purpose should 
be the same as that of the road-surface, and not fine 
material which would soon reduce to powder under the 
loads which come upon it. By careful attention to 
minute repairs in this manner a surface may be kept 
in good condition until it wears so thin as to require 
renewal. 

In case the road be of harder material that will not 
so readily combine when a thin coating is added, the 
repairs may not be so frequent, as the surface will not 
wear so rapidly and immediate attention is not so im- 
portant. It is usually more satisfactory in this case to 
make more extensive repairs at one time, as a larger 
quantity of material added at once may be more 
readily compacted to a uniform surface, the repairs 
taking the form of an additional layer upon the road. 



BROKEN-STONE ROADS. IO9 

Where the material of the road-surface is very hard 
and durable, a well-constructed road may wear quite 
evenly and require very little, if anything, in the way 
of ordinary small repairs until worn out. It is now 
usually considered the best practice to leave such a 
road to itself until it wears very thin, and then renew it 
by an entirely new layer of broken stone placed in the 
same manner as in original construction, on top of the 
worn surface, and without in any way disturbing that 
surface. 

If a thin layer only of material is to be added at one 
time, in order that it may unite firmly with the upper 
layer of the road it is usually necessary to break the 
bond of the surface material before placing the new 
layer, either by picking it up by hand or, if a steam 
roller is in use, by means of short spikes in its surface. 
Care should be taken in doing this, however, that only 
the surface layer be loosened, and that the solidity of 
the body of the road be not disturbed, as might be the 
case if the spikes are too long. 

Sprinkling a broken-stone road surface in dry 
weather may have an important effect in reducing 
the amount of wear and increasing the life of the 
road. If a road carrying considerable traffic is per- 
mitted to become dry and dusty, wear becomes rapid 
and a certain amount of the road metal is blown 
away by the wind, washed away in case of rain, or 
cleaned from the surface as mud. If, however, the 
road be systematically sprinkled, the material ground 
off by the traffic will pack upon the surface, forming 
a cushion which serves to protect it from further 
attrition. In sprinkling the object should be to keep 
the surface damp, and not to flood it by applying too 
large a quantity of water at once. 



CHAPTER VI. 
foundations for pavements. 

Art. 43. Preparation of Road-bed. 

In forming a road-bed upon which to place a pave- 
ment, the earth should be brought at subgrade to the 
form of the finished road-surface, leaving room for the 
superstructure of uniform thickness to be placed upon 
it. Thorough drainage must of course be carefully at- 
tended to when necessary. This has been already dis- 
cussed in Chapter II. 

The road-bed after being brought to the proper grade 
should be thoroughly compacted by rolling before 
placing the pavement. Sometimes in the use of a 
heavy roller, when the material is of a light nature, it 
is shoved forward in a wave before the roller and re- 
fuses to become compacted, in which case a thin layer 
of gravel or small stone placed upon the surface of 
earth before rolling may have the effect of consolidat- 
ing the road-bed under the roller to a hard surface. 

If the material over which the pavement is tc be con- 
structed is a retentive clay which would become soft 
when wet, it is sometimes desirable to excavate the 
clay to a depth of 6 inches or i foot below the grade 
of the road-bed and fill in with sand or some other 
porous and non-retentive material and consolidate this 

no 



FOUNDATIONS FOR PAVEMENTS. Ill 

to form the road-bed. This would seem unnecessary 
in case a sand or gravel foundation is to be used, and 
its necessity in any other case would depend upon the 
likelihood of the road-bed becoming wet, either through 
natural wetness of the soil or in consequence of the 
use of a pavement with open joints or of pervious ma- 
terial. If the clay substructure can be kept dry it will 
sustain the loads which may be carried by the road and 
need not be replaced. 

In constructing a road-bed to bear a pavement the 
same principles would be involved as in the earthwork 
of a common road which has been discussed in Art. 25. 

Art. 44. Purpose of Foundation. 

^'^he chief object of the foundation or base of a 
pavement is to distribute the concentrated loads which 
come upon the surface of the road over a greater area 
of the usually softer and weaker road-bed, in order 
that these loads may not produce indentations in the 
surface. 

In a foundation composed of independent blocks 
extending through its thickness, as in the case of a 
stone-block pavement in which the blocks rest directly 
upon the road-bed or upon a thin layer of sand, the 
load which comes upon the top of any block will be 
distributed over the area covered by the base of the 
block. 

Where the foundation is composed of small indepen- 
dent particles, like sand or loose rounded gravel, with 
no cohesion through the mass, the pressure is distrib- 
uted over the base of a cone whose vertex is in the 
point of application of the load, and the inclination of 



112 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

whose elements depends upon the friction of the par- 
ticles of the material upon each other. In this case 
the area over which the load is distributed varies 
directly as the square of the thickness of the founda- 
tion. Sand, it is to be observed, has also the property 
when confined as in a foundation, on account of its in- 
compressible nature, of adjusting itself to a uniform 
pressure and resisting the deformation of the road-bed. 

If the small pieces composing the foundation are 
cemented together, or held as in masses of angular 
fragments by the interlocking of the angles, the foun- 
dation may act more or less as a whole, causing a distri- 
bution of the load over a considerable area, the extent 
of which will depend upon the resistance of the mass 
to bending. 

The bases most commonly employed for pavenients 
are sand, broken stone, and concrete. Foundations of 
brick and wood are also frequently employed for pave- 
ments of the same materials. 



Art. 45. Sand Foundations. 

Sand foundations as sometimes used under block 
pavements consist simply of a bed of sand from 6 to 
12 inches deep, spread over the road-bed and thor- 
oughly compacted by rolling. 

To obtain the best results the sand should be placed 
in layers of 3 or 4 inches depth and each layer be 
rolled before the addition of the next. This insures 
the equal consolidation of the entire foundation. Un- 
der a heavy roller the sand may usually be compressed 
to J or even f of its original volume. 



FOUNDATIONS FOR PAVEMENTS. II3 

Well-constructed sand foundations arc often very 
efficient for quite severe service. 

Where, as is very common, pavements are set on a 
bed of loose sand, subsequent settlement of the base 
is likely to take place, even if the surface of the pave- 
ment be well rammed during construction. 

Block pavements are also frequently set upon a thin 
layer of loose sand. This, however, can hardly be 
considered a sand foundation, as the sand only acts as 
a cushion to protect the earth of the road-bed from 
direct contact with the blocks. It also at the same 
time may facilitate drainage. 

Art. 46. Bases of Gravel and Broken Stone. 

For light service on a good road-bed a satisfactory 
foundation may frequently be constructed of gravel 
or broken stone at much less expense than would be 
required for a concrete base. A foundation of this 
character should be constructed in about the same 
manner as a broken-stone road, the material being 
spread over the road-bed and thoroughly rolled to 
the required form. The stone or gravel employed 
should contain sufficient small material to fill the 
voids in the aggregate, or a binding material may be 
added to aid in compacting the foundation, and to 
close the interstices so as to prevent any settling of 
the material which is used to support the paving 
surface. 

These foundations are frequently used under brick 
pavements for light traffic with good results. 



114 a text-book on roads and pavements. 

Art. 47. Concrete Bases. 

The best base for general use under pavements is 
without doubt that formed of hydraulic cement con- 
crete. A bed of concrete made of good hydraulic 
cement, well rammed and allowed to set and harden, 
becomes a practically monolithic structure, nearly im- 
pervious to water and possessing a high degree of 
strength against crushing. 

The concrete is formed of a mixture of cement, 
sand, and broken stone or gravel. The proportions 
vary for different work and with the character of the 
materials. With good Portland cement the most 
common proportions for ordinary work are about one 
part cement, three parts sand, and five to seven parts 
broken stone. With the various natural cements the 
proportions vary somewhat, but are usually about one 
part cement, two parts sand, and four or five parts of 
stone or gravel. 

Natural cement is usually employed for this pur- 
pose as being cheaper and possessing ample strength 
for the work, and concrete of the ordinary propor- 
tions with natural cement is to be preferred to that 
made with meagre proportions of Portland cement 
giving about the same strength and cost. Proper 
tests should always be imposed for the purpose of 
securing good cement. 

The sand used for mortar should be clean and 
sharp. The broken stone should be limited in size to 
2 or 2 J inches and should not be too uniform, the 
presence of small material serving to diminish the 
volume of interstices to be filled with mortar. Small 
gravel is sometimes mixed with broken stone for this 



FOUNDATIONS FOR PAVEMENTS. 11$ 

purpose, making it possible to somewhat lessen the 
volume of mortar used in making the concrete. 

In preparing the concrete, the cement and sand 
should first be thoroughly mixed while dry, then the 
proper quantity of water be added, all at once, and 
the mortar be vigorously worked with hoe or shovel 
for two or three minutes, until it comes to a smooth 
and uniform condition. 

The quantity of water should be such as under 
energetic working will reduce the mortar to a soft, 
plastic condition, and should be determined by meas- 
ure. The application of the water from a hose during 
the mixing is objectionable, on account of the diffi- 
culty of regulating the quantity to produce mortar of 
proper consistency. 

When the mixing of the mortar is complete, the 
stone or gravel may be added, and the whole mass 
turned several times with shovels until the mortar is 
evenly distributed through the aggregate. The stone 
should be wet by sprinkling before it is mixed with 
the mortar, in order to cloan the surfaces of dust and 
to prevent the absorption of water from the mortar 
before it sets. 

The concrete, when ready, is placed in position 
and tamped to surface. For this use it is preferable 
that the concrete be of jelly-like consistency, such 
that it will quake under light ramming. If mixed 
more dry, it should be heavily rammed until the 
mortar flushes to the surface, in order to produce 
uniform and compact concrete. 

After completion the foundation should be allowed 
to stand several days before the pavement is placed 
upon it, — three to six days are usually required, — in 



Il6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

order that the mortar may become entirely set. 
During setting the concrete should be protected from 
the drying action of the sun and wind, and should be 
kept damp to prevent the formation of drying cracks. 
Frequently in laying asphalt pavements, a concrete 
is used for the base, which is formed by mixing 
asphaltic or coal tar paving cement with the broken 
stone. This is known as a bituminous base and is 
similar to that mentioned at the end of Art. 46. It is 
commonly constructed by placing the broken stone 
upon the road-bed to a depth of about 4 or 5 inches 
and rolling it to a firm and even bearing, as in the con- 
struction of a broken stone road, after which a coating 
of coal-tar cement is given to it, about one gallon of 
the cement being required for a square yard of the 
base. 

Art. 48. Brick Foundations. 

Foundations of brick have frequently been used 
under brick pavements. The pavement in such cases 
consists of two layers of brick, with sand between, and 
is known as double-layer pavement. These foundations 
are usually formed by placing upon the road-bed a 
layer of sand or gravel 3 or 4 inches thick, which is 
rolled thoroughly to a uniform surface, and then re- 
ceives a layer of brick, commonly laid flat and with 
the greatest dimension lengthwise of the street. These 
bricks are laid as closely as possible with broken joints. 
The joints are filled with sand carefully swept in, and 
the bricks are rammed to a firm bearing. 

Upon this course of brick is placed a cushion layer 
of sand, and then the surface layer. The bricks of the 



FOUNDATIONS FOR PAVEMENTS. II/ 

lower layer may be of a cheaper grade than the sur- 
face-paving brick, as they are not required to resist the 
attrition of travel - 

Art. 49. Sand and Plank Foundations. 

Under many wood pavements, and sometimes under 
brick surfaces, foundations formed of sand and planks 
are used. These foundations differ somewhat in 
construction in various localities, but are essentially a 
bed of sand or gravel, upon which is placed a layer of 
tarred boards which support the surface layer. 

It is common to use a layer of sand 3 or 4 inches 
thick, which is compacted by rolling, after which the 
boards are laid lengthwise of the street close together, 
so as to form a floor upon which the blocks may be 
set. With a brick surface a cushion coat of sand is 
used under the surface layer. 

Sometimes two layers of one-inch tarred boards are 
employed, the lower being laid crosswise of the street 
and the upper lengthwise of it. In other cases, the 
boards of a single thickness are nailed to scantling laid 
across the street and bedded in the sand. The boards 
must in all cases press evenly upon the layer of sand 
that covers the road-bed. 

Art. 50. Depth of Foundation. 

The thickness required for the foundation of a pave- 
ment depends upon the nature of the soil upon which 
it is to rest, and upon the extent and weight of the 
travel to which it is to be subjected. 

On a well-drained road-bed of good material, a depth 
of 6 inches of concrete is usually sufficient, even under 



Il8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

heavy loads. 6 or 8 inches of well-compacted sand 
or gravel will likewise usually suffice. 

When, however, the road-bed is of a retentive ma- 
terial and likely to become wet and soft, the founda- 
tion should possess sufficient strength not to be broken 
through at points where the supporting power of the 
road-bed may be destroyed by water. It must also be 
able to resist the action of frost upon the soil below. 
In such cases 12 inches of concrete may be necessary, 
or 12 to 16 inches of sand or gravel may be desirable. 

Under light traffic with good conditions, a less depth 
may be sometimes used, 4 inches of concrete is fre- 
quently employed to save expense, although 6 is the 
more common depth. 

It is always important that the foundation be suffi- 
cient. The yielding of the base of the pavement means 
its destruction. 

If a firm and durable foundation be employed, the 
surface may be renewed when necessary or changed 
from one material to another without disturbing the 
base, but if the base be weak the surface will be de- 
stroyed. 

The saving of expense should be at the top rather 
than at the bottom of a pavement. 

It may be here observed that no definite prescrip- 
tion for any pavement, either as to choice of founda- 
tion or as to methods of construction can fit all cases. 
What is most successful in one case is quite inappli- 
cable in another. The blind following of particular 
rules by those not conversant with the principles upon 
which they are based has been the cause of many fail- 
ures. Judgment must always be used in weighing the 
local conditions of the problem in hand. 



CHAPTER VII. 
BRICK PAVEMENTS. 

Art. 51. Paving-brick. 

The requisites for a good paving-brick are that it 
shall be hard, tough, and impervious, as well as capable 
of enduring against the disintegrating influences of the 
weather. 

The bricks in most common use are made from fire- 
clay of an inferior quality, or from an indurated clay or 
shale of somewhat similar composition. 

These clays consist essentially of silicate of alumina, 
with usually small percentages of lime, magnesia, iron, 
potash, soda, and sometimes other elements. The 
range of composition for clays in common use is ap- 
proximately as follows : 

Silica 60 to 75 per cent. 

Alumina 10 to 25 

Iron oxide 3 to 8 

Lime o to 4 

Magnesia o to 3 

Potash 0.5 to 3 

Soda o to 2 



In a few cases the quantity of lime is greater vary- 
ing from 8 to 12 per cent. 

1x0 



120 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

When the clay is very nearly pure silicate of alumina, 
it is capable of withstanding a high degree of heat 
without fusing, and is known as fire-clay. As the per- 
centages of other ingredients increase it becomes more 
fusible. The lime, magnesia, potash, and soda act as 
fluxing agents, and the readiness with which the clay 
can be melted depends upon the relative quantities of 
refractory and fluxing materials that it may contain. 

Silica in excess tends to make the brick weak and 
brittle, while too great quantity of alumina causes the 
brick to crack and warp in the shrinking which occurs 
during burning. The proper adjustment of the rela- 
tions between these elements is necessary to good 
results. 

The quantity of lime in the clay is an important 
matter, as the presence of lime in an uncombined state 
in the brick may be productive of disintegration when 
the brick is exposed to the weather. A large percent- 
age of lime in a clay is therefore to be regarded with 
suspicion, although not necessarily as cause for con- 
demnation, as its effect depends upon the state of com- 
bination of the various ingredients of the brick. Mag- 
nesia probably acts in much the same manner as lime. 
Potash and soda are considered desirable elements in 
quantities to properly flux the clay in burning. 

The fineness of a clay is also a matter of importance, 
both because a fine clay will fuse at a lower tempera- 
ture than a coarse one, and because fineness is neces- 
sary to the production of even and close grained brick, 
and therefore conduces to make them tough and im- 
pervious. 

To produce a good paving-brick, a clay is required 
which will vitrify at a high heat, A very refractory 



BRICK PAVEMENTS. 121 

clay will make a porous brick, while if it melts at too 
low a temperature it cannot be burned sufficiently to 
become hard and tough. 

The methods of manufacturing paving-brick vary in 
different localities according to the character of the 
material to be worked. They are quite similar to those 
in use for common brick, only more thoroughly exe- 
cuted. 

The clay is commonly reduced to a fine powder, 
tempered with water and passed through a machine 
that moulds the bricks, which are then dried and after- 
ward burned. Repressed bricks are those which are 
compressed in a mould after coming from the brick 
machine and before drying. 

The process of burning occupies usually from lo to 
15 days. 

The heat is at first slowly applied to expel the water, 
then raised to a high temperature for several days, 
after which the bricks are very slowly cooled. 

There is considerable difference of opinion among 
engineers and manufacturers as to the exact amount of 
burning necessary. It is usually stated that the brick 
should be burned to the point of vitrification, but not 
completely vitrified. The burning must be thoroughly 
done to produce a strong and impervious brick, but 
there is undoubtedly a point beyond which, for some 
brick, further burning causes brittleness. Very gradual 
cooling is also necessary in order to toughen the brick. 

Smoothness and uniformity of texture in a paving 
brick is an important consideration as affecting its re- 
sistance both to crushing and to abrasion. The broken 
surface of the brick should present a uniform appear^ 
ange both in texture and in color. 



122 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

All the bricks used in the same pavement should 
also be of the same degree of hardness and toughness 
in order that the pavement may wear evenly, and to 
this end careful inspection should always be given to 
the bricks proposed for use, and all of those which are 
defective, soft from imperfect burning, brittle from 
overburning or quick cooling, cracked or distorted by 
unequal shrinkage should be rejected. An examina- 
tion of the color and size of the bricks may frequently 
be useful in determining for any particular material 
whether individual bricks have received the proper 
degree of burning, after the engineer has become 
familiar with the make of brick under examination. 
The amount of shrinkage in burning is often a quite 
reliable index of the degree of burning to which the 
material has been subjected, and specifying within 
somewhat narrow limits the variation in size of bricks 
to be used together, may often conduce to greater 
uniformity in the material employed. Some makes of 
brick vary quite appreciably in size for small differ- 
ences in extent of burning, and without materially 
affecting the value of the product, but it is desirable 
to sort them closely and use those of each size by 
themselves. 

The mistake is frequently made of placing too high 
value upon the element of hardness, which when car- 
ried to an extreme is sometimes attained at the ex- 
pense of toughness, the brick becoming brittle afid 
easily shattered. The author (under his guaranty 
on a pavement) has, on one occasion, been obliged to 
replace a small number of hard bricks, which, at the 
time of laying, were supposed to be among the best 
of the lot, on account of their becoming shattered under 



BRICK PAVEMENTS. 12 3 

traffic, while somewhat softer brick from the same kilns, 
the use of which was questioned by the inspector, 
proved quite satisfactory in the same work. 

The sizes of paving-bricks vary considerably as 
made by different manufacturers, the most common 
sizes approximating to those of building brick, varying 
from about 2J to 2f inches in width, 8 to S^ inches 
long, and 4 inches deep, about 56 to 63 bricks being 
required for a square yard of pavement. A few 
makers also produce a brick of about the same size 
but only 3^^ inches deep. A larger size, usually about 
3X9X4 inches, and known as a paving-block to 
distinguish it from the smaller tricky is quite largely 
employed. These usually require from 43 to 47 
blocks per square yard. 

Larger blocks have been tried, but have not come 
into general use, while some manufacturers make 
smaller sizes, requiring 70 to 75 bricks to the square 
yard of pavement. 

Opinions differ as to the best sizes for use in 
pavements, some engineers specifying the smaller 
bricksy others the larger blocks. A good pavement 
can be built of either if proper attention be given to 
selecting the material. The sizes preferred by the 
various manufacturers depend largely upon the 
character of the clay or shale with which they have to 
deal. With some materials the size is limited by the 
distortion of large blocks in burning, and the smaller 
bricks are preferable ; with others, larger blocks may 
be made at less cost in proportion to area of pavement, 
and perhaps with better and smoother work resulting. 
There seems to be no necessity for any increase in the 
usual depth of 4 inches as is sometimes proposed, and 



124 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

it may be possible that the adoption of the depth, 3J 
inches, now frequently used may in many instances 
somewhat lessen the cost of the pavement without 
affecting its length of service. 

Much difference of opinion has been developed 
among engineers as to the advisability of rounding the 
corners of the brick, some requiring that the bricks be 
repressed with corners rounded to a radius of J or f of 
an inch, while others specify square-edge brick, and 
in some instances that they shall not be repressed. 
On the one hand, it is maintained that in service the 
sharp corners will soon be knocked off and worn 
down more roughly and unevenly than if originally 
rounded, while, on the other hand, it is claimed 
that if a rigid filler like Portland cement be used, the 
joint may be filled level with the surface of the brick, 
and be much less likely to chip out than if the joint 
be widened at the top so as to cause the filler to pre- 
sent a thin edge at the sides. Both contentions seem 
reasonable under certain conditions, and the method 
of construction and character of filler used will ordi- 
narily determine the proper form for the brick. 

The desirability of repressing the brick is also a 
much discussed question, it being argued by some that 
the repressing of the material forms a more dense and 
compact block and increases its probable wear in use, 
and by others that the pressure applied to the material 
after it comes from the brick-machine disturbs the 
structure and injures the fibre of the brick, often 
forming laminations which are elements of weakness. 
With some materials this last contention seems to 
have some basis in fact, but in other and probably 
most materials no such condition can be found on ex- 



Brick pavements. 12^ 

amination of the structure of the brick. The views 
of individual manufacturers upon the question seem 
depend mainly upon the kind of material they have 
to work with, and it would be difficult from existing 
data to say that either method necessarily gives the 
best results. Possibly those materials which approach 
most nearly to actual vitrification and are subject to 
considerable shrinkage during the burning are but 
little affected in final density by the compression of 
the block before burning. It should be observed in 
this connection that whatever, may be the value of 
repressing as to its effect upon the quality of the brick 
and wear of the pavement, it undoubtedly has the 
effect with some kinds of brick of giving a smoother 
and better surface to the pavement by producing a 
more regular and uniformly shaped brick. 

In order to give sufficient space between the bricks 
for the joint-filling, some manufacturers make re- 
pressed bricks with lugs on one side to hold them a 
given distance apart when laid in the pavement. The 
wisdom of this under ordinary circumstances seems 
doubtful as small joint-space is usually desirable, and 
experience shows that bricks laid close, even if care- 
fully driven up, will usually give plenty of space for 
filling. Spacing-lugs are seldom required in specifica- 
tions, but engineers have sometimes required their use 
for work on steep grades with the idea of giving 
better foothold to horses than the thin joints would 
afford. There may be some advantage in this, and 
some pavements so constructed on grades of above 
eight per cent have given satisfactory results, the lugs 
usually projecting about half an inch from the face of 
the brick, but in the author's own experience he has 



126 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

been unable to notice any difference in the use of the 
pavement with or without the wide joints, all being 
laid with level-edge brick. 

Repressed bricks and blocks are frequently made 
with a groove or two, extending lengthwise of the 
brick on each side and sometimes across the ends, for 
the purpose of keying the blocks together when filled 
with the joint-filler. This may be an aid to rigid 
construction, though not necessary to good work. 
It is usually limited to the larger blocks, which fre- 
quently have thin lugs, as well as the grooves, and 
are known as groove- and lug-blocks. They are well 
calculated to give a very firm construction. 

Art. 52. Tests for Paving-brick. 

To determine the probable durability of brick de- 
signed for use in paving, mechanical tests may be 
applied which will show the relative rank of different 
samples in their most important characteristics. It is, 
however, a matter of considerable difficulty to set a 
standard to which the brick should be required to con- 
form, or to determine, from the behavior of the bricks 
under test, the relative value of various samples which 
it may be desired to compare. 

The tests ordinarily proposed or used for this pur- 
pose are those of crushing strength, transverse strength, 
abrasion and impact, absorption, and specific gravity. 
The relative importance of these tests and the weight 
which should be given to their results is a matter con- 
cerning which considerable difference of opinion has 
been developed amongst engineers, and practice varies 
considerably. The National Brick Manufacturers* 



BRICK PAVEMENTS. I27 

Association have considered the matter, and in 1895 
appointed a committee which in 1897 reported a set 
of rules for making the tests, with resolutions ex- 
pressing their views as to the relative importance and 
reliability of each. These rules, which were some- 
what modified in 1900, are very commonly followed 
and furnish a standard method of testing. 

Crushing Test, 

The recommendations of the commission for con- 
ducting this test are as follows: 

**I. The crushing test should be made on half- 
bricks, loaded edgewise, or as they are laid in the 
street. If the machine used is unable to crush a full 
half-brick, the area may be reduced by chipping off, 
keeping the form of the piece to be tested as nearly 
prismatic as possible. A machine of at least 100,000 
pounds capacity should be used, and the specimen 
should not be reduced below 4 square inches of area 
in cross-section at right angles to direction of load. 

*'II. The upper and lower surfaces should prefer- 
ably be ground to true and parallel planes. If this is 
not done, they should be bedded in plaster of Paris, 
while in the testing-machine, which should be allowed 
to harden ten minutes under the weight of the crush- 
ing planes only, before the load is applied. 

'* III. The load should be applied at a uniform rate 
of increase to the point of rupture. 

'' IV. Not less than an average obtained from five 
tests, on five different bricks, shall constitute a stand- 
ard test." 

The result of a compressive test of stone or brick 
depends very largely upon how it is made, and the 



128 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

results of tests are only properly comparable with 
others made in the same manner and with equal care. 
The use of plaster beds as suggested above, it is 
thought, conduces greatly to regularity of result in the 
work of different men, as it tends to reduce the effect 
of differences in the accuracy of dressing the surfaces 
of contact. The size of the test-piece is also impor- 
tant, the strength usually increasing as the size in- 
creases. Small pieces, ij- or 2-inch cubes, are often 
employed because of the large force necessary to crush 
a whole or half brick, although where machinery exists 
capable of doing it the larger tests entail much less 
work in preparing specimens and also yield much 
more satisfactory results. Where small specimens are 
used it is to be observed that the unit strength will 
not be the same as for larger ones, and must be judged 
by a different standard. In the preparation of speci- 
mens it is better, when possible, to saw than to break 
them by chipping, in order not to injure the block by 
the shock of the blows. 

The commission in their discussion concluded that 
no connection had been shown between high strength 
and the qualities necessary for a good paving material, 
and adopted the following resolution : 

** Whereas, From the experimental work done so 
far by this commission, or by others so far as is known 
to us, in the application of the cross-breaking and 
crushing tests to paving-bricks, it is not possible to 
show any close relationship between the qualities nec- 
essary for a good paving material and high structural 
strength as indicated by either of these tests, — 

' * Resolved^ That for this reason the commission rec- 
ommends that these tests shall be considered as purely 



BRICK PAVEMENTS. I29 

optional in the examination of paving nnaterial, and 
not necessary as a proof of excellence." 

It is to be observed that the actual crushing strength 
of a brick is not a matter of special importance in so 
far as any danger of the crushing of the material in the 
pavement is concerned, as no stress can there come 
upon it under ordinary circumstances which would en- 
danger even a very weak specimen from direct crush- 
ing. It is thought, however, that to some extent the 
value of the brick is indicated by its resistance to 
crushing, coupled, of course, with a proper examina- 
tion of its other necessary attributes. A brick which 
possesses a high crushing strength is not necessarily a 
good paving-brick, as it may at the same time be brit- 
tle or of such composition as to easily disintegrate 
under the action of the weather ; but one that yields 
to a low crushing strength is usually weak in wearing 
qualities and not fit for the purpose. For this reason 
this test is commonly included in specifications pre- 
scribing tests, although it is recognized that the rela- 
tive wearing qualities of various makes of brick can- 
not be graded by its results. A good paving-brick, 
in the form of a 2-inch cube, will usually show a re- 
sistance to crushing of not less than 10,000 pounds 
per square inch. Much higher values are sometimes 
used in specifications, but their advantage is at least 
doubtful. 

Transverse Test. 

The transverse strength is tested by supporting the 
brick upon two knife-edges near its ends and bringing 
a load through a third knife-edge upon the middle of 
the brick. The test may be made upon any ordinary 



130 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

testing-machine by providing the necessary knife- 
edges, but, like the compression test, requires care in 
manipulation to get good results. It is specially im- 
portant that the brick have a perfectly even bearing 
upon the supports before the application of the load, 
in order that it may not be subjected to a twist under 
the load. The method adopted by the commission 
for this test is as follows : 

I. Support the brick on edge, or as laid in the 
pavement, on hardened steel knife-edges rounded 
longitudinally to a radius of 12 inches and trans- 
versely to a radius of one-eighth inch, and bolted in 
position so as to secure a span of six inches. 

II. Apply the load to the middle of the top face 
through a hardened steel knife-edge, straight longi- 
tudinally and rounded transversely to a radius of one- 
sixteenth inch. 

III. Apply the load at a uniform rate of increase 
till fracture ensues. 

IV. Compute the modulus of rupture by the for- 
mula 

3 «;./ 



/ = 



2 bd^^ 



in which /= modulus of rupture in pounds per 
square inch ; 
w = total breaking load in pounds ; 
/ = length of span in inches = 6 ; 
If = breadth of brick in inches ; 
d =: depth of brick in inches. 

V. Samples for test must be free from all visible 
irregularities of surface or deformities of shape, 



BRICK PAVEMENTS. I3I 

and their upper and lower faces must be practically 
parallel. 

VI. Not less than 10 brick shall be broken and the 
average of all be taken for a standard test. 

The commission included this test with the crush- 
ing test in the recommendation that the test was to 
be considered optional and " not necessary as a proof 
of excellence." This testis easier to conduct satis- 
factorily and probably gives, in general, a more reli- 
able indication of the value of the material than the 
crushing test. It calls into play the tensile as well 
as compressive strength of the brick. The interior 
structure is shown by the break, and an opportunity is 
given to judge of the uniformity and homogeneous 
character of the material. 

The fracture of a tough and homogeneous speci- 
men under a transverse load should be a clean break 
through the middle of the brick, and a close observa- 
tion of the breaks may frequently be of considerable 
assistance in forming an idea of these qualities, al- 
though they may not be directly represented by the 
load required to break the specimen. The shattering 
of the brick in breaking, or an irregular break extend- 
ing from the point of application of the load to one 
of the points of support, usuallj'" indicates brittleness 
of the material. 

The modulus of rupture of good paving-bricks 
commonly ranges between 2000 and 3000 pounds per 
square inch, sometimes reaching 3500 or even 4000 
pounds. It is usually somewhat greater for brick 
laid fiat than for brick on edge. 



132 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Abrasion Test, 

In the convention of 1897 the Brick Manufacturers' 
Association adopted a method for this test consisting 
in rattling a given charge of bricks in a cylinder rotat- 
ing about its axis, which is horizontal, and depending 
for its result upon the impact and abrasion of the 
bricks upon each other. In 1900, however, after 
more fully considering the matter, the test was modi- 
fied and a smaller charge of bricks, with the addition 
of a charge of cast-iron shot, was recommended as 
more nearly representing the conditions of practice 
and giving results more in accord with experience. 

The method finally recommended by the Associa- 
tion is as follows : 

**/. Dimensions of the Machine. — The standard 
machine shall be 28 inches in diameter and 20 inches 
in length, measured inside the rattling-chamber. 

** Other machines may be used varying in diameter 
between 26 and 30 inches, and in length from 18 to 
24 inches; but if this is done, a record of it must be 
attached to official report. Long rattlers may be cut 
up into sections of suitable length by the insertion of 
an iron diaphragm at the proper point. 

**//. Construction of the Machine, — The barrel 
shall be supported on trunnions at either end ; in no 
case shall a shaft pass through the rattling-chamber. 
The cross-section of the barrel shall be a regular 
polygon having 14 sides. The heads and staves 
shall be composed of gray cast iron, not chilled or 
case-hardened. There shall be a space of one-fourth 
of an inch between the staves for the escape of dust 
and small pieces of waste. Other machines may be 



BRICK PAVEMENTS. 133 

used having from 12 to 16 staves, with openings 
from one-eighth to three-eighths of an inch between 
staves; but if this is done, a record of it must be 
attached to the ofificial report of the test. 

*'///. Composition of the Charge. — All tests must 
be executed on charges containing but one make of 
brick or block at a time. The charge shall consist of 
nine paving-blocks or twelve paving-bricks, together 
with three hundred pounds of shot made of ordinary 
machinery cast iron. This shot shall be of two sizes, 
as described below, and the shot-charge shall be com- 
posed of one-fourth (75 pounds) of the larger size and 
three-fourths (225 pounds) of the smaller size. 

'''IV, Size of the Shot. — The larger size shall weigh 
about 7^ pounds and be about 2\ inches square and 
^\ inches long, with slightly rounded edges. The 
smaller size shall be cubes of i\ inches on a side, with 
rounded edges. The individual shot shall be replaced 
by new ones when they have lost one-tenth of their 
original weight, 

** V. Revolutions of the Charge. — The number of 
revolutions of a standard test shall be 1800, and the 
speed of rotation shall not fall below 28 nor exceed 
30 per minute. The belt-power shall be sufficient to 
rotate the rattler at the same speed whether charged 
or empty. 

** VI. Condition of the Charge. — The bricks com- 
posing the charge shall be dry and clean and as 
nearly as may be possible in the condition in which 
they were drawn from the kiln. 

" VII. Calculation of the Result. — The loss shall 
be calculated in the per cents of the weight of the 
dry brick composing the charge, and no result shall 



134 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

be considered as official unless it is the average of two 
distinct and complete tests made on separate charges 
of brick." 

The commission regard this as the most important 
test to be applied to paving-brick, and in fact it is 
the only one having their endorsement. It seems 
reasonable to suppose that this test gives more nearly 
than the others a determination of the value of the 
brick for use in a pavement. 

It is quite true that the action to which the brick 
is subjected in a test of this character is different 
from the wear to which it is subjected when firmly 
held in the pavement, but the qualities necessary to 
resist wear in the two cases are very similar. We 
may form an idea of whether a material is suitable for 
the proposed use from such experiments, although no 
definite idea of the amount of wear that it will en- 
dure can be obtained from them. It should also be 
pointed out that the method of estimating the loss of 
the brick, from abrasion tests made in this manner, as 
percentages of the total weight of brick, can, in the 
comparison of different bricks, only give correct re- 
sults when the bricks compared are of the same size 
and shape. A brick with rounded edges evidently 
could not properly be compared with one with sharp 
edges by this method, and some engineers have di- 
vided the test into two periods for the purpose of 
separating the knocking off of the corners and pre- 
liminary rounding of the brick from the later abrasion 
upon the rounded surfaces which would be more 
nearly comparable for different specimens. If, in the 
test, the loss in the rattler during the first half-hour 
be separated from that during the second half-hour, 



BRICK PAVEMENTS. 135 

the latter will be found to be much less affected by 
the form of the brick. 

In comparing bricks of different sizes it should be 
noted that a small brick presents more surface for 
abrasion than a large one in proportion to its volume, 
and the results of such comparisons would be con- 
siderably modified in some instances if the results be 
stated in terms of exposed surface instead of percent- 
age of volume. With square-edged brick during the 
early period of the test, when corners are being 
chipped off, the loss is probably more nearly propor- 
tional to length of edges than to surface or volume, 
which would be still more to the disadvantage of the 
small brick. Care is therefore necessary in drawing 
conclusions from such tests concerning the relative 
values of different materials that all the conditions 
which may affect such conclusions be fully under- 
stood. 

A rattler for testing paving-brick has been patented 
by Mr. Gomer Jones, formerly City Engineer of 
Geneva, N. Y., in which the brick are held in the 
circumference of the rattler, and a charge of 150 
pounds of cast-iron cubes, i^ inches on the edge, is 
placed in the rattler and revolved. The machine is 
the ordinary rattler, 24 inches in diameter, with staves 
made to clamp the brick end to end, leaving the brick 
exposed about one inch in depth on the side. The 
action is that of picking and abrading the surface 
by light blows, and is claimed to develop the defects 
and pick out soft spots in the brick much better than 
the ordinary method, and avoid breaking the brick by 
heavy blows. The treatment given by this apparatus 
is certainly more like the conditions under which th^ 



136 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

brick is used in the pavement than that given by the 
standard method. 

Absorption Test, 

This test is made by weighing the specimen dry, 
then saturating it with water, weighing again, and 
stating the absorption as a percentage of the dry 
weight The Commission of the Brick Manufac- 
turers Association oppose the use of this test, but 
recommend the following procedure for the test when 
used : 

I. The number of bricks for a standard test shall 
be 5. 

II. The test must be conducted on rattled bricks. 
If none such are available, the whole bricks must be 
broken in halves before treatment. 

III. Dry the bricks for 48 hours at a temperature 
ranging from 230° to 250° F. before weighing for the 
initial dry weight. 

IV. Soak for 48 hours, completely immersing the 
brick. 

V. After soaking and before reweighing wipe the 
brick until free from surplus water and practically 
dry on the surface. 

VI. Reweigh the samples at once on scales which 
are sensitive to i gram. 

VII. The increase in weight due to absorption is to 
be calculated in percentage of the dry weight of the 
original bricks. 

The commission also adopted the following resolu- 
tion : 

''''Resolved, That, in the opinion of the commission, 
any paving-brick which will satisfy the requirements 



BRICK PAVEMENTS. 1 3/ 

of reasonable mechanical tests will not absorb sufficient 
water to prove injurious to it in service. We therefore 
recommend that the absorption test be abandoned as 
unnecessary, if not actually misleading." 

The purpose of this test, when made, is to insure 
the proper burning of the brick to a compact and non- 
absorbent structure. It is probable, as claimed by the 
commission, that these qualities will always be shown 
by the other tests, and that this one is not of very 
great importance, but in many instances it may give 
useful information. A good paving-brick will not 
usually absorb more than 4^ or 5^ of water, but the 
amount of absorption depends largely upon the nature 
of the material from which the brick is made. Many 
of the shale bricks absorb less than i^ of water if 
properly burned, while some of the so-called fire-clay 
bricks when of equally good quality will absorb 3^ or 
4^. A specification which would insure the proper 
burning of the one class would exclude the best of 
the other class. A limit to the amount of absorption 
allowable is, however, commonly set in specifications. 

The requirement of drying 48 hours is probably, in 
most instances, sufficient and reduces the moisture in 
the brick so that the further loss from continued 
drying would be very slight, but the saturation of the 
brick will not usually be accomplished by immersing 
for 48 hours. Some bricks will in that time have 
taken up but a small part of the water they would 
finally absorb, and much longer time would be neces- 
sary to give a complete indication in this particular. 
Some experiments by Mr. Harrington of St. Louis, 
the results of which were presented to the Brick 
Manufacturers' Association, showed a considerable 



138 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

change in the quantity of water absorbed by some 
bricks through a period of 24 weeks, and a consider- 
able variation in the rate of absorption by different 
bricks. 

The application of the test as proposed may serve 
to show whether the absorption is within the proper 
limits for a paving-brick, and when properly applied 
to particular makes of brick may indicate the degree 
of burning, although it may not be of much value in 
the comparison of the qualities of different bricks 
where each shows results within reasonable limits. 

Specific-Gravity Test. 

A test for specific gravity is sometimes included 
in specifications with a view to insuring the burning of 
the brick to the proper density. 

In consequence, however, of the variation of bricks 
made from different materials it does not seem feasible 
to adopt any requirement for general use which would 
be of much value, and as the same qualities are de- 
termined by other tests it seems unnecessary. The 
Commission of the Brick Manufacturers* Association 
recommend the abandonment of this test. 

Comparison of Tests, 

Where tests are required in specifications, certain 
limiting values may be assigned to what may be 
shown by each test, and the brick be required to 
reach at least this limit on all the tests, or certain 
tests may be regarded as of greater importance and 
bricks showing high values in these be accepted, 
though not so satisfactory in others. The most re- 



BRICK PAVEMENTS. 1 39 

liance is usually placed upon the rattler test; the 
tests for crushing, transverse strength, and absorp- 
tion being usually employed with that test, some en- 
gineers preferring one, some another, of these. 

When it is desired to compare by tests the relative 
merits of various makes of brick, as in the case of com- 
petitive tests, it becomes necessary to determine the 
comparative values of the results of the different tests 
and give to each a weight in proportion to its impor- 
tance. For this purpose various formulas have been 
proposed in which the results of the separate tests are 
combined into a single term representing the supposed 
value of the brick. Prof. J. B. Johnson proposed the 

formula F = (25 - i?) + (3 - A) + -^+ ^ 



1000 4000 

This has been used to some extent in specifica- 
tions. The formula of the St. Louis Board of Pub- 

,. , . __ 10 , I , Z' C 

he Improvements is *^ = ^- H ^ n + 



Rg^ 4 A 2000 ' 4000* 
While Mr. H. A. Wheeler proposed the formula 

V= (iS-R)6+(7-A)4-] 1 . In all of these 

^ y I v/ /t I 220 1000 

F— value of brick; R = loss in rattler in percentage 
of weight of brick; T' = the transverse strength in 
terms of load per inch of width ; T = modulus of rup- 
ture per square inch ; C = crushing strength per square 
inch. With the range of value commonly obtained 
for paving-brick, Johnson's formula gives a weight of 
60 or 70 per cent to the rattler test, 10 to 15 per cent 
each to the absorption and crushing tests, and 8 
or 10 per cent to the transverse test ; Wheeler's 
formula gives more weight than Johnson's to the rat- 
tler test and less in proportion to the transverse 



I40 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

test. The St. Louis formula gives a weight of about 
30 per cent to the results of the rattler test and 4$ per 
cent to those of the crushing test. 

The rattle test is, without doubt, the most impor- 
tant of these tests, as calling into play more nearly than 
the others the qualities necessary to wear in the pave- 
ment ; but in using such a method of comparison the 
conditions which may affect the results of that test as 
already outlined, and the limitations within which 
such tests are properly comparable, should be kept in 
mind. The wisdom of placing such supreme confi- 
dence in the results of this test, and rejecting the use 
of the others even as aids to the judgment, as seems 
to be done by the Commission of the Brick Manu- 
facturers' Association, is at least open to question. 

Art. 53. Foundations for Brick Pavements. 

A brick pavement should have a firm foundation. 
As the surface is made up of small independent blocks, 
each brick must be adequately supported from below, 
or the loads coming upon it may force it downward 
and cause unevenness. The wear of the pavement 
depends very largely upon the maintenance of a smooth 
even surface, as any unevenness will cause the bricks to 
chip on the edges, and also produce impact from the 
loads passing over the pavement. 

The best foundation for a brick pavement is doubtless 
one of concrete, laid after the manner given in Art. 47. 
For light or moderately heavy traffic, such as that of 
the ordinary small city, the concrete is usually placed 
6 inches thick. If the traffic be very heavy 9 inches 
may be necessary, and where from any cause the road- 



BRICK PAVEMENTS. I4I 

bed is not firm it may be advisable to still farther in- 
crease the depth. 

Under comparatively light traffic a foundation of 
gravel or broken stone as mentioned in Art. 46 may be 
used. This foundation should, however, usually be 
employed only where traffic is light and the road-bed 
good. 

The double-layer pavement (see Fig. 22) consists of 
a foundation made by placing a layer of sand or gravel 
3 to 5 inches thick upon the road-bed, rolling it 
thoroughly and laying a course of bricks upon it. The 
bricks are laid flat with their greatest dimension length- 
wise of the street, as explained in Art. 48. 

This foundation has been more extensively used 
under brick pavements than any other, and has oftei: 
given satisfactory results. It is now largely giving 
place to concrete in the better class of work, and in 
many cases under light traffic its economy is question- 
able, as the layer of gravel would often answer equally 
well without the lower layer of bricks. The best base 
to use for a particular work must usually be largely 
determined by the availability of various materials. 

Art. 54. Construction of Brick Pavement. 

The work to be performed in laying a brick pave- 
ment, after the preparation of the road-bed and 
placing the foundation, as indicated in Chapter VI and 
Art. 53, consists in placing a cushion coat of sand over 
the foundation, laying the brick upon the sand cushion, 
ramming or rolling the bricks to a uniform surface and 
bearing, culling all broken or imperfect brick, filling 
the joints between the brick, and finally cleaning the 
pavement and opening it to traffic. 



142 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Sand Cushion. — The sand cushion consists usually 
of a layer of sand varying, in the practice of different 
engineers, from ^ to 2^ inches in thickness over the 
surface of the foundation. The most common prac- 
tice is to make the sand cushion i|- or 2 inches thick. 
It should be deep enough to admit of the brick being 
driven to a smooth surface, and to take up any in- 
equalities in the surface of the foundation and differ- 
ences in thickness of brick. When a very thin cushion 
layer is employed it is necessary to secure much 
greater accuracy in forming the surface of the founda- 
tion, and it is much more difficult to uniformly bed the 
bricks than when the usual thickness is used. It has 
also been claimed that the thicker sand-bed has a 
marked tendency to diminish the rumbling of the 
pavement. This, however, is perhaps rather doubt- 
ful. 

In forming the sand-bed the sand is spread over the 
foundation a little deeper than the bed is to be left, 
and is then drawn off to a smooth surface by the use 
of a form, cut to the desired shape of the surface, 
which extends across the street, and slides on the 
curbs or on stringers laid lengthwise of the street as 
may be convenient. The making of a good firm bed 
requires that considerable sand shall be pulled off 
from all parts of the bed, and the sand should always 
be two or three inches deep against the front of the 
form when drawing it to cut the bed. In order to 
accomplish this, without failing to cut a perfect sur- 
face through the form leaving the guides and riding 
up on the sand, considerable weight is required on the 
form when drawing it. 

The sand for a cushion should be clean and free 



BRICK PAVEMENTS. 



143 



from pebbles, which prevent the formation of a smooth 
bed, and possibly also cause the breaking of the bricks 
in ramming the surface. 

When the sand cushion is i^ or 2 inches deep, an 
allowance of about half an inch is necessary for settle- 
ment in driving the bricks to surface. 

Laying the Brick. — The bricks in a street pavement 
are usually laid on edge in courses across the street, 
each alternate course being begun with a half-brick to 
break joints in the courses. This is illustrated in Fig. 
21, which represents a pavement as constructed for 
heavy traffic on concrete foundation. 




Fig. 21. 

In many cases the gutter-bricks are turned with the 
greatest dimension lengthwise of the street, with the 
object of facilitating the flow of surface-water in the 
gutter. The advantage of this is doubtful, as it has 
the effect of breaking the bond of the pavement be- 
tween the gutter-bricks and roadway. This is shown 
in Fig. 22, which represents the construction of a 
double-layer pavement with brick and gravel base, as 
has been commonly used under light or moderate 
traffic. 

In laying the bricks the men stand on the pavement 



144 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



already laid and, beginning at a curb, lay three or four 
courses across the street at once, the bricks being 
wheeled and piled on the edge of the finished work 
by laborers working continually in advance of the men 
laying. Wheeling over the newly laid bricks should 
be done on planks, to prevent driving the bricks out 




.- i;^^ ^ 




Fig. 22. 

of surface. The courses may be kept straight and 
close together by driving back each block of eight or 
ten courses ; a straight piece of plank four or five feet 
long being held by a handle on top against the side of 
the course of bricks and lightly struck with a small 
sledge. 

After the bricks are laid across the street the end 
joints are tightened by forcing back each course with 
an iron bar, and closers are fitted into the end spaces. 
Considerable skill is required in this part of the work 
to quickly and accurately fit the closers without wast- 
ing the material. 

Surfacing the Pavement. — After the surface layer 
of bricks is in position it should be swept clean and 
rammed or rolled to a smooth and uniform surface. A 
five- or six-ton roller may be employed passing three 
or four times over the surface, or a wooden rammer 



BRICK PAVEMENTS. I45 

loaded with lead to a weight of 80 or 100 pounds may 
be used by striking upon a plank laid lengthwise of 
the street. The plank should be ten or twelve feet 
long by about a foot wide and three inches thick, and 
used only so long as it retains its form and solidity. 

When the pavement has been brought to a surface 
a careful inspection should be made and all defective 
or broken brick removed and replaced, a pair of brick- 
tongs being used for the purpose, and all low bricks 
or low spots being raised and brought to surface. 
A straight-edge is desirable in determining surface, as 
the appearance is often deceptive to the eye, and a 
slight variation in color of brick is frequently mistaken 
for an irregularity of surface. Sometimes the pavement 
is sprinkled and soft bricks picked out by observing 
whether they hold moisture; this method should be 
used with caution and with full knowledge of the 
material, as sometimes a comparatively slight absorp- 
tion will show quite markedly. 

Filling the Joints, — There is much difference of 
opinion amongst municipal engineers concerning the 
best material to use in filling the joints in a brick 
pavement. The materials commonly employed are 
sand, Portland-cement grout, and asphaltic or coal-tar 
paving-cement. Certain patent fillers of more or less 
the same character are also sometimes employed. 

Sand Filler. — In using sand as a filler, a thin layer 
of sand is spread over the pavement and raked or 
swept into the joints until they are thoroughly filled. 
In some instances the sand is artificially dried before 
putting it upon the bricks, but ordinarily, in mod- 
erately dry weather, the sand may be spread in a thin 
layer on the bricks and allowed to dry before sweep- 



14^ A TEXT-BOOK ON ROAHS AND PAVEMENTS. 

ing in. After the joints are well filled a light layer 
of sand is placed on top of the pavement and it is 
opened to traflfic. The jarring of the traffic will 
cause the sand to settle more or less in the joints for 
a considerable time, and the sand cover should be 
retained for several weeks. The sand used for filling 
should be fine and sharp, free from loam and dirt. It 
must not pack or cake on top of the brick under traf- 
fic. In many instances sand has been used as a filler 
with satisfactory results and given good service even 
under moderately heavy traffic. It makes a practi- 
cally impervious joint and holds the bricks quite 
firmly in place. It seems desirable in the use of 
sand filler to employ round-edge bricks, as the edges 
are not held so firmly as with a rigid filler, and if 
sharp are more likely to be chipped off, while the 
round edges aid in thoroughly filling the joints with 
the sand. 

Bituminous Filler, — When bituminous filler is em- 
ployed it is melted in kettles on the street and 
poured hot into the joints. The paving-cement is 
applied at a temperature of 250° to 300° Fahr., and 
should only be applied when the bricks are dry. 
After the joints are filled a light layer of sand is 
spread over the surface, and serves under the traffic 
to clean the surface from any surplus tar which may 
be smeared over it. 

In some instances sand is used with paving-cement 
for filling, being separately heated and mixed with 
the paving-cement in filling the joints. The bitumi- 
nous filler is not so rigid as that made from Portland 
cement, but does not give the rumbling sound to the 
pavement, and by some engineers is preferred to the 



BRICK PAVEMENTS. 1 47 

sand filler, although by many thought not to hold 
the bricks so firmly in place. It makes the pave- 
ment quite impervious. 

Portland-cement Filler. — For filling joints with 
Portland cement a grout composed of equal parts 
of cement and sand is commonly employed. This 
grout is mixed in a tight box to a condition such that 
it will readily flow into the joints, and is swept in 
with brooms until the joints are thoroughly filled. 
The easiest method of securing the complete filling of 
the joint is probably that of applying the grout in 
two parts, mixing the first part very wet and filling 
the joints nearly full. As the grout begins to stiffen, 
the draining out of the water causes it to settle some- 
what, but thoroughly fills and seals the lower part of 
the joint. The second part may then be mixed a 
little more stiff and the upper part of the joint be 
readily filled flush with the top of the bricks. 

In handling the grout it is necessary that it be 
mixed quickly and applied at once without giving it 
time to settle, in order that it may retain its consist- 
ency and no separation of its materials take place. 
A pavement so filled becomes practically a mono- 
lithic mass, as the bricks are firmly held together and 
the joint is filled flush with the edges of the bricks 
with a material which soon becomes about as hard as 
the bricks themselves. 

A serious objection to the cement filler is the 
rumbling usually resulting from filling the pavement 
solidly with cement grout, which is doubtless due to 
the expansion of the mortar in the joints. This 
has been doubted by some, on the ground that the 
rumbling is no worse in hot than in cold weather j 



148 A TEXT-BOOK ON ROADS AND PAVEMENTS 

but the expansion which causes rumbling is probably 
that due to the natural swelling of the cement mortar 
rather than that due to temperature. It is well 
known that Portland-cement mortar when kept in 
a damp condition expands considerably for several 
months after it has set. It is also subject to consid- 
erable changes in dimension with variations in moist- 
ure, and probably the least effect of expansion, rather 
than the greatest, is to be expected in hot, dry 
weather. 

The rumbling of the pavement may be largely ob- 
viated by using expansion-joints along each curb and 
at intervals across the street. These joints are com- 
monly made by putting a wooden strip between the 
courses of brick in laying and afterward removing the 
board and filling the joint with asphaltic or coal-tar 
paving-cement before applying the cement grout to 
the pavement. 

To be efficient these joints should not be less than 
f inch when spaced 50 feet apart. Such joints will 
usually be nearly closed in a few months, the paving- 
pitch being forced out by the expansion. After the 
completion of the pavement it should stand at least 
a week or ten days before admitting traffic, to allow 
sufficient time for the cement to harden. During 
this time it should not be exposed to hot sun or per- 
mitted to dry out too much ; commonly a light 
coating of sand is spread over it, or sometimes it is 
dampened by frequent sprinklings. 



BRICK PAVEMENTS. 1 49 



Art. 55. Maintenance of Brick Pavements. 

The maintenance necessary for a brick pavement 
consists in keeping it clean and carefully watching it, 
especially during the first year or two years, to see that 
no breaks occur due to the use of defective bricks in 
the surface or to insufficient support from the founda- 
tion at any point. When any unevenness from either 
of these causes appears, it should be at once rectified 
before the pavement becomes irregularly worn in con- 
sequence. 

While, as already stated, the utmost care should 
always be taken to use only material of a uniform 
quality in the surface of the pavement, still under the 
closest inspection some inferior material may be used, 
which will only be shown when wear comes on the 
pavement, and unless then removed at once it will 
cause the evenness of the surface to be impaired about 
it. Irregular support from the foundation will be 
less likely to occur in good construction, but its effect 
will be similar to defective material, the sinking of in- 
dividual bricks producing uneven wear. Weak spots 
in the foundation may sometimes be caused, where con- 
crete foundation is not employed, by surface-water 
which is permitted to pass through the joints, saturat 
ing the sand or gravel beneath and causing it to move 
under concentrated loads. For this reason the joints 
should be observed during the early wear of the pave- 
ment in order to remedy any case where they may not 
have been properly filled. 

Where a brick pavement has been constructed of 
good material and kept in good surface during the 



150 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

early period of use, it may then reasonably be expected 
to wear out without any considerable expense for small 
repairs. The length of time the pavement may be ex- 
pected to wear depends upon the quality of the ma- 
terial and the methods of construction. For the 
moderate traffic of many of the smaller cities, and 
lesser streets in the large cities, brick has shown an 
endurance which indicates it to be a satisfactory and 
economical material, and it is not improbable that by 
careful attention to proper construction it may be used 
for even heavier traffic. 



CHAPTER VIII. 
ASPHALT PAVEMENTS. 

Art. 56. AsPHALTUM. 

ASPHALTUM is a mineral pitch which occurs in 
a number of localities widely distributed over the 
surface of the earth. It is supposed by most authori- 
ties to be the result of the decomposition of vegetable 
matter, although by some it is considered to be of vol- 
canic origin. It consists, in its natural state, of bitumen 
with a small percentage of foreign organic matter and 
mixed with more or less mineral earth, and varies 
according to the nature of the bitumen from the soft 
viscid condition of mineral tar to a hard brittle sub- 
stance of glassy appearance and conchoidal fracture. 
It also occurs in a solid state as a rock impregnated 
with bitumen, which will be separately considered in 
another article under the head of rock asphalt. 

The asphaltum used for street pavements in this 
country is obtained for the most part from the island 
of Trinidad, W. I., and from the state of Bermudez, 
Venezuela. This asphaltum is known as lake asphalt 
or as land asphalt according to the source from which 
it is derived. Lake asphalt is found in large deposits 
known as the pitch lakes. The lakes cover a consider- 
able area, — in Trinidad about 100 acres ; in Bermudez 

i5i 



152 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

several hundred, — and the pitch seems to be, or have 
been, forced upward from below through fissures in the 
rock or craters. The pitch upon contact with the air 
gives off gas and gradually hardens. In the lakes 
proper the asphaltum is more or less in motion, and 
excavations in the surface are soon filled by the flow 
of material from the sides and bottom. The pitch near 
the centre of the lake at Trinidad is more soft than 
near the sides, and it has been supposed that the 
supply from subterranean sources still continues to 
some extent. It has also been found that the surface 
of the lake is higher in the centre than at the sides, 
and that the general elevation of the surface has been 
lowered somewhat by the large quantities of material 
which have been removed from it. 

The so-called land asphalt from Trinidad is found in 
vicinity of the lake, and is a harder material than the 
lake asphalt, probably from longer exposure to the air. 
It may have been derived either from overflow of the 
lake or from independent subterranean sources the 
action in which has now ceased. (For a complete 
description of the Trinidad pitch deposits see the 
*' Report of the Inspector of Asphalts and Cements of 
the District of Columbia " for 1891-92.) 

Asphaltum similar in character to that already men- 
tioned occurs at many other places. Mines are worked 
in Cuba and Peru, and large deposits are found in 
Mexico. It occurs at a number of places in Europe, 
while the bituminous mortar of the ancient Chaldean 
constructions was of this character, and beds of as- 
phaltum are still found in that country from which it 
may have been obtained. In the United States de- 
posit? of asphaltum ^X^. fQwn<4 v^ California, Utah, 



ASPHALT PAVEMENTS. 153 

and other places. Those of California are extremely 
varied in character, and some of them are extensively 
employed for pavements throughout the United States. 

The crude asphaltum usually contains considerable 
water as well as earthy and vegetable impurities. It is 
heated in a boiler to 300° or 400^ Fahr., the water 
being driven off, and the impurities settling to the 
bottom or forming a scum on top. The liquid as- 
phaltum is then drawn off and is known as refined 
asphalt. This refined asphalt may contain more or 
less mineral or earthy matter distributed through it in 
a finely divided state. Refined Trinidad asphalt may 
contain 52 to 56 per cent of pure bitumen, while Ber- 
mudez asphalt is said to contain 97 per cent. 

The refined asphalt is brittle at ordinary tempera- 
tures, and possesses little cementitious value. To re- 
duce it to a condition from which it may be easily 
compacted in the pavement, it is heated to a tempera- 
ture of about 300° Fahr. and mixed with the oil re- 
siduum obtained from the distillation of petroleum. 
This mixture is very thoroughly worked, so as to form 
a material of uniform consistency. The product is then 
known as asphaltic paving cement. 

Great care is necessary in mixing the paving cement 
to properly proportion the ingredients, as the value of 
the cement depends upon their nice adjustment. Both 
materials are quite variable in their properties, and 
continual tests are necessary of the materials employed 
as well as of the resulting product, in order to obtain 
a cement of uniformly good quality. The quantity of 
oil necessary varies with the nature of the asphaltum, 
being less as the asphaltum is of a more plastic and 
less refractory nature, 



154 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

The surface material for a pavement of asphaltnm is 
formed by mixing asphaltic paving cement, prepared 
as already described, with sand, or with sand and pow- 
dered limestone. The proportions of the various in- 
gredients depend upon their character and upon the 
requirements of the pavement. In order to obtain 
good results it is necessary that the exact nature of 
each of the ingredients be determined, and the proper 
amounts used. With Trinidad asphaltum the surface 
material ordinarily contains about lO per cent of pure 
bitumen. 

The sand used for this purpose is usually very fine, 
60 per cent being sometimes required to pass a sieve 
of 60 meshes per linear inch, and all of it through one 
of 30 meshes. It is important also that the sand be 
clean and free from loam or clay. The carbonate of 
lime is used in the form of fine powder. 

In forming the surface material the sand and paving 
cement are separately heated to a temperature of 
about 300° Fahr. and mixed, while hot, in an apparatus 
which thoroughly incorporates them into the mixture. 
When powdered limestone is used it is added cold to 
the hot sand before mixing with the hot paving 
cement. 

As may be readily seen, the selection of asphaltum 
for paving purposes, as well as the process of forming 
the surface material, is a matter requiring very great 
care and an intimate knowledge of the characteristics 
of the materials to be employed. In order to secure 
good results it is quite essential that careful examina- 
tion be made of every mixing of the material for the 
surface, both by testing the materials before they are 
used and the product after it is formed. Analysis of 



ASPHALT PAVEMENTS. 155 

every lot should be made as well as consistency tests. 
Experience is the only guide, and there is no method 
of judging of value in such work other than by the re- 
sults of former work of the same kind. 

Variations in the quality of asphaltum are attributed 
to the character as well as the quantity of bitumen 
that it contains. This bitumen is made up of 
two parts, the first of which, called petrolene, is the 
oily and cementitious material ; the other, called 
asphaltene, is the hard material lacking, in the ce- 
menting properties. The varying proportions of these 
ingredients in the bitumen determine the temperature 
at which it will melt, and the facility with which it may 
be used for paving purposes. A certain proportion of 
asphaltene is probably necessary to give the material 
sufficient stiffness at ordinary temperatures ; but too 
large a quantity makes it lacking in plasticity and 
cementing properties, and renders it necessary to use 
a large proportion of residuum oil in preparing the 
asphaltic cement. 

The residuum oil also varies considerably in'character, 
and the quantity to be used in each case depends 
somewhat upon the character of the oil. The object 
aimed at is to get a cement of given consistency, which 
is measured by the penetration of a needle, at a stand- 
ard temperature and under a standard weight. In 
forming the paving cement it is necessary that the 
materials be constantly agitated in order that the oil 
and asphaltum may be intimately mixed, and that the 
mass of cement may be uniform throughout. 

For making a paving cement, in some cases where 
American asphalt has been used, a maltha, or liquid 
bitumen, has been substituted for the residuum oil to 



156 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

reduce the asphaltum to plasticity. This maltha is a 
nearly pure bitumen, similar in character to the asphal- 
tum, but differing in that the bitumen contains a high 
percentage of the hydrocarbon known as petrolene 
and but very little asphaltene, the proportion between 
the two being such as make the bitumen liquid at 
ordinary temperatures. 

The composition of surface material for asphalt 
pavements must be varied to suit the conditions under 
which each is built. The variations of temperature 
to which the pavement may be subjected are of special 
importance, and the nature of the traffic may also have 
an influence. The surface must not soften under the 
heat of summer, and yet must be sufficiently plastic 
not to become brittle and chip off in cold weather. 
For light traffic the material may be more soft in warm 
weather than under heavy traffic, as it is not so liable 
to cutting under the loads. 

The quantity of paving cement used in the surface 
material may depend somewhat upon the consistency 
adopted for the cement. If it be stiff a larger per- 
centage may be used, with the same effect as to the 
softening of the surface in summer than if it be soft. 
The common proportions of ingredients employed in 
forming the surface material are approximately as fol- 
lows : 

For Trinidad Asphalt. For Bermudez Asphalt. 

Asphaltic cement 12 to 15 per cent. 9 to 10 percent 

Sand 83 to 70 " 71 to 60 " 

Carbonate of lime 5 to 15 " 20 to 30 " 

In some cases stone-dust, formed by crushing a hard 
stone, such as granite, to about the dimensions of a 



ASPHALT PAVEMENTS. 157 

fine sand, is substituted for a portion of the sand and 
carbonate of lime. 

The proper treatment in any instance can only be 
determined by a careful study of the materials to be 
used, the climatic conditions, and the service required. 

Art. 57. Rock Asphalt. 

Rock asphalt, as commonly used in paving, consists 
of limestone naturally impregnated with bitumen in 
such proportion as to form a material which may be 
softened by the action of heat and again consolidate 
when cooled if brought under pressure. 

This rock is mined at several places in Europe, 
notably at Seyssel, France ; Travers, Switzerland ; 
Ragusa, Sicily, and Vorwohle, Germany. It is usually 
composed of nearly pure carbonate of lime, impreg- 
nated with from 7 to 20 per cent of bitumen. It 
occurs in veins, after the manner of coal, is hard at the 
ordinary temperatures of the mines, and is quarried by 
the use of explosives. 

The preparation of the surface material of rock 
asphalt consists only -in crushing and grinding the 
rock to powder and heating the powder to drive off tlie 
water and soften it, so that it may be compacted in 
the roadway. The powder is heated to a temperature 
of from 200° to 300° Fahr., and is applied while hot in 
laying the surface. 

Natural rock asphalt, suitable for paving purposes, 
usually contains from 9 to 12 per cent of bitumen. If 
it contain much more than this it is apt to become 
soft in warm weather. If it contain less it will not 
consolidate properly or bind well in the pavement. 



15^ A TEXT-BOOK ON ROADS AND PAVEMENTS. 

The rock should be of fine even grain, and have the 
bitumen uniformly distributed through it. In form- 
ing the surface material for rock asphalt pavements, 
the rock from different mines is commonly mixed in 
such proportions as to give about lO or 12 per cent of 
bitumen to the mixture, thus making a harder surface 
than would be obtained by the use of the rich rock 
alone, as well as less likelihood of softening. No other 
material is mixed with the rock in forming the 
surface. 

In determining a mixture of asphalt rock, as in the use 
of the lake asphalt, the local conditions of climate and 
trafHc must be considered, and the quantity of bitumen 
be so proportioned as to remain solid in summer and 
not become brittle and lose cohesion in winter. Ex- 
perience with the material and exercise of great care 
in the determination of proper proportions is therefore 
essential to success in the construction of any asphalt 
pavement. 

In the use of bituminous limestone for sidewalks 
and many other purposes where a plastic material is 
required, the rock asphalt powder is mixed with an 
additional quantity of bitumen, or asphaltum, sufficient 
commonly to give a product containing 15 to 18 per 
cent of bitumen. This product is known as asphalt 
mastic in Europe. For use in sidewalks the mastic is 
melted and mixed with sand or gravel to form a wear- 
ing surface. 

A sandstone impregnated with bitumen occurs at a 
number of localities in the United States. This stone 
has been applied to some extent in paving, in some- 
what the same manner as the European material. It 



ASPHALT PAVEMENTS. I59 

occurs in California, Kentucky, Texas, and other 
localities. In California and the Indian Territory a 
sand is also found impregnated with asphaltum, while 
bituminous limestones similar in nature to the European 
asphalts occur in Utah, Texas, and the Indian Terri- 
tory. 

The California asphaltic sand is handled by crush- 
ing the material and then extracting the bitumen by 
dissolving it with gasolene and conveying the liquid 
through pipes to the refinery, where it is distilled and 
the gasolene pumped back to be used again. The 
California bituminous sandstone has been used to a 
considerable extent in the California cities quite suc- 
cessfully, although in much of the early work varia- 
tions in the composition of the material and the 
proper methods of using it were not understood and 
some failures naturally resulted. 

The asphaltic sandstones of Kentucky have been 
used for pavement by treating in a manner similar to 
that used with the European asphalts. The quantity of 
bitumen in the rock is usually low, about 6 to 9 per cent, 
and needs the admixture of a richer material, although 
some of it contains a higher percentage. It has some- 
times been used in combination with German rock 
asphalt with good results, and also by mixing with 
bituminous limestone from Texas. 

The Texas bituminous limestone has been used for 
paving, as have also the asphalts of the Indian Terri- 
tory. The asphalts as use'd contain a higher per- 
centage of bitumen than is common in paving mate- 
rial, and are employed by mixing the asphaltic sand 
with the bituminous limestone. 

As shown above asphalts are widely and generously 
distributed, and there is in this country a wide range 



l60 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

of materials of this character, most of which probably 
may be used for pavement, but much of which is of 
more value for other purposes. The composition of 
each of these materials varies considerably both in the 
quantity and the nature of the bitumen, and the value 
and proper method of use for each can be determined 
only by experiment and experience. 

Art. 58. Asphalt Blocks. 

Asphalt paving blocks are commonly formed of a 
mixture of asphaltic cement with crushed limestone. 
This limestone is crushed to sizes of ^ inch in diameter 
or less, and mixed with the asphaltic paving cement 
formed as described in Art. 56, in such proportions 
as that the product contains about 10 per cent of 
bitumen. 

The materials are heated to a temperature of about 
300° Fahr., and mixed while hot in an apparatus 
arranged to secure the even distribution of the ingre- 
dients through the mass. The thorough incorporation 
of the various materials in the mixture is of first im- 
portance in producing homogeneous and uniform 
blocks, while the quality of the materials used needs 
as careful inspection as in the case of the surface mate- 
rial for sheet pavements. 

When the mixing is complete, the material is placed 
in moulds and subjected to heavy pressure, after which 
the blocks are cooled suddenly by plunging into cold 
water. 

These blocks have usually been made larger than 
paving-bricks, the common size being 12 inches long, 
4 inches wide, and 5 inches deep. They are laid in the 
same manner as brick, as closely in contact as possible, 
and driven together. Under the action of the sun and 
the traffic, the asphalt blocks soon become cemented 



ASPHALT PAVEM i:\TS. l6l 

together, through the medium of the asphaltic cement, 
and form, Hke the sheet asphalt pavements, a practi- 
cally imperivous surface. 

They are commonly used on streets of light trafHc 
only, as the blocks as heretofore constituted wear 
rapidly under heavy trafific. They are usually laid 
upon a foundation of sand or of sand and gravel, and 
on account of the impervious nature of the surface 
may often give satisfactory results on such a founda- 
tion, where a more pervious block pavement or a sheet 
pavement would require more efHcient support. 

A large amount of pavement, of blocks made prac- 
tically as described above, has been laid in this country, 
particularly at Baltimore and Washington, and have 
shown good durability in wear under moderate and 
light travel. 

These blocks have the advantage over sheet asphalt 
for the smaller cities, that the blocks may be formed 
at a central-point and shipped ready for use to the site 
of the proposed pavement, and that no special plant 
need be erected in each town where they are to be 
constructed. 

In forming the asphalt block pavement the road-bed 
is brought to subgrade in the ordinary manner and 
rolled, leaving room for the pavement of uniform thick- 
ness to be placed upon it. A layer of gravel 4 or 5 
inches deep is then placed and rolled, with a cushion 
coat of sand i to 2 inches, and then the paving blocks. 
The blocks are pressed together in the courses by the 
use of a lever, and the courses driven against each 
other with a maul to reduce the joints as much as 
possible. A coating of sand is given to the surface of 
the pavement, and it is rammed to a firm and uniform 
surface, as in the case of brick. 



1 62 a text-book on roads and pavements. 

Art. 59. Foundations for Sheet Pavements. 

As a sheet asphalt surface has no power to sustain 
loads, acting only as a wearing surface, which must be 
held in place from below, it is essential that it be 
placed upon a very firm, unyielding foundation. It is 
consequently nearly always placed upon a concrete 
base, which is commonly formed of hydraulic cement 
mortar and broken stone, prepared as described in 
Art. 47. In the use of this base, it is necessary that 
the mortar be fully set, and the concrete thoroughly 
dry before the asphalt is laid upon it, as the placing of 
the hot surface material upon a damp foundation will 
cause the blistering and possible disintegration of the 
surface by the steam generated from the base by the 
heat of the material. 

For moderate or heavy traffic in cities, the concrete 
base is commonly made 6 inches thick. For lighter 
trafBc a less depth, 4 inches or 5 inches, is sometimes 
employed. The depth necessary will depend upon the 
nature of the road-bed as well as the weight of the 
traffic. It should be greater as the subsoil is less firm 
and well drained. 

Frequently the concrete for the foundation is formed 
of asphaltic or coal tar paving cement instead of 
hydraulic cement mortar. It is then known as bitu- 
fninous concrete, and the foundation is called a bitumi- 
nous base to distinguish it from the ordinary hydraulic 
base. The advantage claimed for the bituminous base 
is that the foundation and surface material become 
joined into a single mass, with the effect of anchoring 
the surface and preventing the formation of weather- 
cracks and wave-surfaces, which sometimes occur when 



ASPHALT PAVEMENTS. 1 63 

the hydraulic base is used, under a light surface layer, 
in consequence of the lack of bond between the hy- 
draulic concrete and the asphalt surface. Another 
reason for the use of this base is that it is cheaper than 
the hydraulic base. 

An intermediate layer known as the binder course 
is now commonly added to the foundation, or rather 
placed between the foundation and surface layers. 
This layer is usually formed of coal-tar or asphaltic 
paving cement, mixed with small broken stone, not 
more than i inch in diameter, about one gallon of the 
cement being required to i cubic foot of stone. 

The materials are mixed hot and laid and rolled in 
the same manner as the surface layer. This binder 
becomes consolidated with, and gives added depth and 
strength to, the surface ; thus having a tendency to pre- 
vent the cracks and wave-surfaces which may other- 
wise appear in the surface when used upon an hydraulic 
base. 

The hydraulic base is usually preferred to the bi- 
tuminous base on account of its forming an unyield- 
ing structure, not likely to be forced out of place by 
the weight of the traffic at any point where the support 
of the road-bed may be weakened, while the bituminous 
concrete has not the strength to resist deformation uii 
der heavy loads unless uniformly supported. The join- 
ing of the base and surface into one mass, as is effected 
by the bituminous base is also a disadvantage when the 
pavement is to be resurfaced, as with the hydraulic 
concrete base the surface may be easily stripped off, 
and a new surface placed without injury to the founda- 
tion. 



164 a text-book on roads and pavements. 

Art. 60. Construction of Sheet Pavements. 

The construction of asphalt pavements in this 
country is, in the main, in the hands of two or three 
large corporations, and methods of construction vary 
but little, the differences in the various pavements being 
principally due to differences in the composition of the 
materials used. 

In constructing the pavement after the completion 
of the foundation as indicated in the preceding article, 
the surface material is brought to the place where it is 
to be used in a large kettle and applied in a hot, semi- 
plastic condition and thoroughly consolidated by roll- 
ing. The tools with which the material is handled are 
kept hot, hot rakes being ordinarily employed for 
spreading it, and hot rollers for the first compacting. 

Sometimes, as already indicated, a binder course is 
inserted between the base and surface layers. This 
binder course is usually 1^ inches thick, composed of 
coal-tar cement and small broken stone, and applied in 
the same manner as the surface layer. This construc- 
tion has been considerably used in Washington, and a 
pavement so constructed is known as the combination 
pavement. 

In some cases where the binder course is omitted, 
the surface is applied in two layers, of which the lower, 
known as the cushion coat, is made from h, inch to 
I inch thick when compacted, and contains a higher 
percentage of paving cement than the surface layer. 
This layer having more of the cementitious material 
adheres more strongly to the hydraulic base, and forms 
a tie between foundation and surface. 

When a bituminous base is employed the cushion 



ASPHALT PAVEMENTS. 165 

coat is generally considered unnecessary, as the surface 
layer will join directly with the base. The binder 
course is, however, frequently used in this case to give 
added strength and weight to the pavement. 

The surface coat, prepared as described in Arts. 56 
and 57, is usually applied so as to be about i^ to 2^ 
inches thick when compacted in the pavement. When 
a binder course is employed about i^ inches, otherwise 
2 inches to 2j- inches. 

In the construction of rock asphalt pavements, which 
have been almost exclusively used in Europe, it is com- 
mon to ram the surface layer with hot rammers, and 
smooth it off with smoothing-irons, while in this country 
small hot rollers have usually been employed. The 
practice of the rock asphalt companies has also differed 
from that of those using lake asphalt, in that the latter 
continue rolling the surface with heavy rollers until it 
is hardened and shows no mark, while the European 
practice is to roll more lightly and leave the final com- 
pression to be given by the traffic. 

In Europe foundations of hydraulic cement concrete 
are exclusively used, with the surface layer usually 
directly in contact with it. This system is also most 
commonly used in this contry, the standard pavement 
being formed of an hydraulic base 6 inches thick with 
a single surface layer 2^ inches thick when compacted, 
or where lighter construction is admissible, an hydrau- 
lic base 4 inches thick is used with a surface layer 2 
inches in thickness. 

In all asphalt pavements it is customary during the 
rolling to give the surface a coating of hydraulic cement, 
\yhich is usyally swept lightly over the surface. 



l66 a text-book on roads and pavements. 

Art. 6i. Vulcanite or Distillate Pavement. 

Numerous attempts have been made to construct a 
pavement by the use of coal-tar as a cementing material 
in place of or in conjunction with asphaltum. But few 
of these have met with any degree of success. Coal- 
tar by itself, as most commonly employed, is soon dis- 
integrated by the action of the weather ; it is also 
strongly affected by temperature, becoming soft in hot 
weather and brittle in cold weather. 

Pavements in which the wearing surface is composed 
of a mixture of coal-tar and asphaltum have in some 
cases given good results in practice. These pavements 
are known as vulcanite or coal-tar distillate pavements. 
They are much cheaper than asphalt. They are said 
to be somewhat less slippery, and to resist better where 
exposed to dampness. The vulcanite surface, however, 
is not so durable under wear, and it requires very great 
care in construction to produce a surface of uniformly 
good quality, because of the possible variations in the 
nature of the coal-tar used. 

In the preparation of the surface material for distil- 
late pavement as it has been used in Washington, a 
paving cement is used containing 70 to 75 per cent of 
coal-tar paving cement and 25 to 30 parts refined as 
phaltum. The construction of the pavement is in other 
respects similar to that of the combination asphalt 
pavement on a bituminous base. As commonly con- 
structed the pavement includes a 4-inch bituminous 
base, a i-J-inch binder-course, and a surface of tar dis- 
tillate I J inches thick. The material for the wearing 
surface for this pavement, according to the specifica- 
tions of 1892, was formed as follows. 



ASPHALT PAVEMENTS. 1 6/ 

Clean sharp sand 63 to 58 per cent. 

Broken stone or rock dust. .23 to 28 

Paving cement 1 3 to 1 5 

Hydraulic cement 0.9 

Slaked lime 0. 1 5 

Flour of sulphur o. i 

The materials are heated to 250° Fahr. and mixed 
hot, then laid after the manner of asphalt. 

Art. 62. Maintenance of Asphalt Pavements. 

To give good service asphalt pavements must be 
kept clean. On account of the smooth surface and 
absence of joints, cleaning may be readily accomplished ; 
and the presence of dirt, especially in wet weather 
when it is likely to cause the surface to remain damp, is 
liable to cause the asphalt to rot. More than any 
other pavement, therefore, the durability and wear of 
an asphalt surface depends upon its cleanliness. The 
presence of dirt upon asphalt in damp weather is also 
important in its effect upon the slipperiness of the 
pavement. 

Small repairs of any breaks that may occur in an 
asphalt surface may be easily made, and such repairs 
should be constantly attended to in order to keep the 
surface in good condition. Small breaks will rapidly 
extend if they are not repaired at once. In making 
repairs to the surface of the pavement it is necessary to 
cut away the surface for a short distance about the im- 
perfect spot, stripping the surface from the foundation 
and cutting the layer down square at the edges, after 
which a new piece of surface may b'e introduced to fill 
the hole in the same manner that the original surface 



l68 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

was constructed. Such a patch may ordinarily be put 
on so as to make joints that will join perfectly with the 
old pavement and not show where it has been placed. 
When a surface has become so worn that patches would 
be numerous, the old surface may be stripped off and 
a new one placed upon the original foundation. When 
repairs are to be made upon a pavement having a bitu- 
minous base it is more difficult to cut out the holes in 
satisfactory shape, as there is no well-defined joint be- 
tween the base and the surface layers. 

The repairs that may be required upon an asphalt 
pavement depend, of course, upon the solidity of con- 
struction and the nature of the surface material. There 
is so great variation in the materials employed for the 
wearing surface that, as would naturally be expected, 
very considerable difference in wear is shown by dif- 
ferent pavements. Asphalt pavements for the most 
part, as has been stated, are built by corporations em- 
ploying corps of expert workmen, and the plan usually 
adopted is to require the contractor to keep the pave- 
ment in repair for a certain length of time without 
charge and afterwards to maintain it for a certain longer 
period at a fixed annual price. This makes it an object 
for the contractor to do good work, and is the most 
effective way of securing it where so many elements of 
uncertainty enter. 



CHAPTER IX. 
WOOD PAVEMENTS. 

Art. 63. Wood Blocks. 

Wood for pavements should be close-grained and 
not too hard. It should be as homogeneous as pos- 
sible in order that the wear may be uniform, and soft 
enough that it may not wear smooth and slippery. To 
give good service in wear the wood should be pene- 
trated by water as little as possible and show good 
resistance to decay under the action of the weather. 

Wood for this use should be sound and well seasoned. 
The blocks should always be subjected to careful in- 
spection. All sapwood needs to be removed in order 
to lessen the liability to early decay, and blocks con- 
taining shakes and' knots should be rejected. 

In the United States cedar has been most largely 
used for this purpose and has proved to be a quite 
satisfactory wood for such use. Yellow pine and tam- 
arack have also been employed for pavements to some 
extent at the North, and cypress, juniper, cottonwood, 
and mesquite at the South. These varieties have all 
been used with some success, and can be made to fur- 
nish a fairly good paving material. 

Oak and other hard woods are less likely to wear 
evenly in the pavement, become smooth and slippery, 
and bear less well the exposure to the weather and in- 

169 



170 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

fluences tending to cause decay in the wood. In Wash, 
ington, D. C, a pavement of hemlock blocks was at one 
time constructed on quite an extensive scale, but proved 
unsatisfactory and was soon destroyed. It does not 
appear, however, to have been a well-constructed pave- 
ment or of properly selected material. 

In Australia hard-wood blocks have been quite ex- 
tensively used and are reported as giving good service, 
although they are admitted to be somewhat slippery in 
wet weather. Australian Karri and Jarrah woods are 
employed, and it is claimed for them that they show 
unusually great resistance to wear and are not soon 
affected by decay. 

In London, where wood pavements have been very 
extensively employed, Swedish yellow deal is com- 
monly placed at the head of the list of woods in value, 
yellow pine and Baltic fir being also largely used and 
considered good in use. The Australian woods above 
mentioned have also been used to some extent in Lon- 
don, and are said to have given very satisfactory ser- 
vice, showing greater resistance to wear than deal or 
pine, although somewhat expensive. 

Wood pavements are commonly constructed of blocks 
set with the fibres vertical, so that wear comes upon the 
ends of the fibres and has no tendency to split pieces 
off from the blocks. Cedar blocks are used in the form 
of whole sections of the tree, on account of the liability 
of the wood to split off between the layers when cut to 
a rectangular shape- They are usually of an approxi- 
mately cylindrical form, varying from 4 to 9 inches in 
diameter and 5 to 8 inches in depth. Commonly the 
whole section is used witli the bark removed, giving 
blocks somewhat irregular in shape. In some cases the 



WOOD PAVExMENTS. I7I 

blocks are, however, cut to a true cylindrical form, the 
sapwood as well as the bark being cut away, by passing 
them through a set of knives which are gauged to 
turn out cylinders of given size. Several sets of knives 
are employed, giving blocks of varying sizes, each block 
being cut sufficiently to eliminate all sapwood with as 
little waste of good material as possible. The use of 
sapless blocks increases the life of the pavement by 
augmenting the resistance of the material both to wear 
of the traffic and to the disintegrating influences of the 
atmosphere and moisture. 

Wooden paving-blocks other than cedar are usually 
of rectangular form, 8 to 12 inches long, 3 to 5 inches 
wide, and 5 to 8 inches deep. As the blocks are usu- 
ally laid in courses, the width as well as the depth must 
be constant for the same work. It is usual to cut the 
blocks from plank of uniform thickness, — ordinarily 3 
inches, — as the narrow blocks give a better foothold for 
horses in damp weather, and also are more easily 
settled to a firm and even bearing in the pavement. 

Hexagonal blocks at-e also sometimes used. In a 
mesquite pavement constructed at San Antonio, Texas, 
the blocks are hexagonal in form, the tops being 
slightly smaller than the bottom, the diameter varying 
from 4 to 8 inches, with a depth of 5 inches. 

The tendency of recent practice in constructing 
wood pavements has been in the direction of making 
the depth less than was formerly used. Five inches is 
now a very common depth. 

Deep blocks are usually a waste of material, as in 
most cases not more than 2 or 2^ inches at most can 
be worn from the pavement before it is replaced, even 
if the traffic be sufficient to wear it out before it rots. 



1/2 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

In the use of the AustraHan hard woods in London 
a less depth of block has been tried and found satis- 
lactory, and a depth of about 3J inches is recommended 
by some of the engineers. 

Art. 64. Foundations for Wood Pavements. 

The foundation which has been most commonly used 
in the United States for wood pavement is that com- 
posed of a layer of boards upon sand, as described in 
Art. 49. This foundation has been used in a number 
of places with fairly good results, and, under light 
trafific, where the first cost of the pavement must be 
low, its use may sometimes be advantageous. This 
form of construction has the disadvantage of being 
less firm than the others usually employed, as well as 
that of being perishable in its nature. 

The life of the pavement is therefore likely to be 
less than upon a more firm and durable base, as the 
destruction of the surface of the pavement may be 
caused by the yielding of the foundation. There have 
been instances recorded where a base of this kind has 
worn out two or more surface layers, and there are 
others in which the failure of the foundation planks is 
the beginning of the destruction of the surface. Much 
depends upon the locality and the quality of the work. 

On the better class of wood-block pavements, a 
foundation of concrete is usually employed. This 
gives firm support to the blocks, and admits of 
even wear upon the surface of the pavement. A dur- 
able foundation also has the advantage that when the 
surface layer is worn out, the pavement may be resur- 
faced without renewing the foundation. 



WOOD PAVEMENTS. 1/3 

In using a concrete foundation, a cushion coat of 
sand is commonly employed on top of the concrete in 
which to bed the blocks in order that they may be 
brought to an even surface. Sometimes a thin layer 
of cement mortar is used in place of the sand upon the 
concrete; and in London some pavements have been 
constructed with a thin layer, about ^ inch, of asphalt 
mastic over the concrete, the blocks resting upon the 
mastic. 

Broken-stone and gravel bases are also frequently 
employed under wood blocks, a layer of boards being 
usually placed over the broken stone to form an even 
bearing for the bases of the blocks, although some- 
times the blocks are bedded in a cushion coat of sand, 
as with the concrete foundation. In Duluth, a Telford 
foundation has been employed under wood, laid in the 
same manner as for a broken-stone road. A layer of 
gravel was placed upon the Telford pavement and 
rolled to a smooth surface, after which the wood blocks 
were laid directly upon the gravel. The reason given 
for the application of this foundation instead of con- 
crete in this instance is that the road-bed is of soft 
material, which in many places could not be compacted 
by the use of a heavy roller before the placing of the 
concrete, while the stones of the Telford foundation 
are forced to a firm bearing and give a uniform sup- 
port. This difficulty of a soft road-bed has been some- 
times met in other places by rolling a thin layer of 
gravel or broken stone into the surface of the road-bed, 
the forcing of the stones into the soil causing it to be- 
come compact and firm, after which the concrete may 
be placed in the usual manner. 

It is perhaps even more important that the founda- 



174 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

tion for a wooden pavement be firm and unyielding 
than with other kinds of block pavement. Any small 
motion due to the flexibility of the base is likely to 
split the blocks, and if through the yielding nature of 
the foundation some of the blocks are forced out of 
surface so that the surface becomes slightly uneven, 
the wear will be very greatly increased over what would 
be the case if the foundation were firm and immovable. 

Art. 65. Construction of Wood Pavements. 

In the construction of pavements of cylindrical 
blocks, or whole-tree sections, as in the common cedar 
pavement of the United States, blocks of varying sizes 
are usually employed, being set in contact with each 
other, the smaller blocks between the larger ones, in 
such a way as to leave the spaces between blocks as 
small as possible. With blocks varying from 4 to 8 
inches in diameter, this arrangement gives good foot- 
hold for horses, and at the same time reduces to a 
minimum the wear due to the blows caused by wheels 
sinking into the joints where large spaces exist between 
the blocks. 

The common arrangement of cedar blocks is shown 
in Fig. 23, which represents a section of pavement as 
ordinarily constructed on a sand and board foundation. 

In the use of rectangular blocks, the blocks are set 
with their longest dimension transverse to the length 
of the street. They are usually arranged in courses 
across the street, being placed close together in the 
courses, and arranged to break joints in adjoining 
courses. Between courses a joint is usually made J to 
4 inch in width, for the purpose of affording a foothold 



WOOD PAVEMENTSc 



175 



to horses. In the older pavements of this character a 
much wider joint was employed, some as much as an 
inch in width, with the idea that they were necessary 
to secure proper foothold. Experience has shown, 
however, that the wide joints are not necessary ; and it 




Fig. 23. 



is now commonly agreed that where, as is now com- 
mon, the blocks are limited to a width of 3 inches, a 
joint J inch in width is sufificient for the purpose. As 
in the case of round blocks, durability is greater where 
the joints are as small as possible, and the liability of 
the fibres of the blocks to spread is eliminated. 

The tendency in practice is toward a continual dim- 
inution of the width of the joint, and some pave- 
ments have been constructed in London in which the 
courses of blocks are placed in contact with each other. 
These are reported to have given good results in ser- 
vice, and to be advantageous in increasing the durabil- 
ity of the pavement. In some cases, where the pave- 
ments are laid with close joints, an expansion joint ^ 
inch in width is provided for every 30 inches of length, 
in order to provide for the swelling of the blocks. In 
other cases, however, this is said to have been omitted 
without injury to the pavement. 



176 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

The method of setting rectangular blocks is shown 
in Fig. 24, which represents a wood-block pavement on 
a concrete foundation, as commonly constructed. 

In laying a pavement of this kind, a course of blocks 
is first set across the street, and then a strip of wood 
of the thickness of the joint is set against the row o 
blocks and left until the next course is placed, or 




Fig. 24. 

sometimes spuds with heads of the thickness of the 
joints are driven to the head in the side of each block, 
and the next row of blocks are set against the spuds. 

Where blocks are set in courses across a street, it is 
necessary that allowance be made at the curb or gutter 
for the expansion of the blocks. This is usually ac- 
complished by leaving an open or sanded joint until 
the blocks have done swelling. 

The gutter blocks are very commonly turned with 
their lengths along the street, and sometimes the course 
next the curb is left out temporarily and filled with 
sand to provide for swelling. 

Various methods are employed for filling the joints 
between the blocks. It has been the common practice 
in the construction of the cheaper wood pavements in 
the United States to fill the joints with sand and gravel, 
sometimes with a coating of tar, or in some cases the 



WOOD PAVEMENTS. 177 

joint is partially filled with tar and then completely 
filled with sand or small gravel. The objection to this 
method is that it does not make an impervious joint, 
which in a wood pavement, and especially with the 
cheaper foundations, is a matter of the utmost im- 
portance. 

The best practice seems to be to fill the lower part 
of the joint for about one half the depth with coal-tar 
paving cement and the upper part with hydraulic cement 
mortar. The cement mortar gives a harder wearing 
surface than where the entire joint is filled with pitch. 
It also protects the pitch from the softening action of 
the sun in warm weather. Where very narrow joints 
are employed, the greater wear of the tar cement may 
not be of so much importance. Some engineers fill the 
entire joint with coal-tar cement, while others use the 
cement grout alone. The object in all cases should be 
to make a road-surface as nearly impervious to water 
as possible. 

The coal-tar paving cement used for the purpose of 
filling joints is the same as that used for brick pave- 
ments. It is usually formed of coal-tar residuum mixed 
with creosote oil or with tar, but it varies widely in 
character in different places. Sometimes asphalt i 
used, or asphalt mixed with coal-oil, but more frc 
quently the name asphalt is incorrectly applied to coal- 
tar products, v/hen it is called asphaltic cement. It is, 
of course, always applied hot to the pavement. 

When the ordinary coal-tar cement filling is employed, 
the joints are first filled nearly full of sand or gravel, 
which is rounded down with a bar, after which the hot 
cement is poured in until the joint is well filled- 

When cement grout is used it should consist of a 



1 7^^ A TEXT-BOOK ON ROADS AND PAVEMENTS. 

rich mortar, i part Portland cement to 2 parts sand, or 
I part natural cement to i part sand. 

In London, where the wood blocks are set upon a 
layer of asphalt, it is customary to fill the lower part of 
the joint with melted asphaltic cement and the upper 
part with cement grout. This method is not, however, 
extensively employed. 

The method of procedure in constructing a wood 
pavement depends upon the kind of foundation em- 
ployed. When a concrete base is used, a cushion coat 
of sand about one inch in thickness is usually spread 
evenly over the concrete. Upon this layer of sand the 
blocks are set, close together if round blocks, or in rows 
as already described if rectangular blocks are used. 
The blocks are then rammed to a firm and even bear- 
ing by the use of heavy wooden rammers, the joints 
are filled with gravel and paving cement or grout, as 
the case may be, a layer of gravel is spread over the 
surface, and the pavement is opened for traffic. Most 
of the well-known London wood pavements are con- 
structed in this manner, the blocks being of fir or deal, 
and cut to a rectangular shape, although, as already 
stated, some of the later ones are built with close joints 
from which the gravel filling is omitted. 

Where the sand and board foundation is employed, 
the best practice is probably represented by the method 
pursued at Chicago, which is approximately as follows: 
A layer of sand 3 inches thick is placed upon the road- 
bed, which has been compacted by rolling. The sand 
is rammed or rolled until well compacted, and the 
foundation layer of 2-inch hemlock planks laid length- 
wise of the street, resting at their ends and middles 
upon stringers I inch by 8 inches bedded firmly in the 



WOOD PAVEMENTS. 1/9 

sand. Upon this foundation the cedar blocks are set 
close together, the joints are filled with small gravel 
well rammed, and the pavement is then flooded with 
hot tar cement so as to fill the interstices in the joints. 
A coating of gravel one inch thick is then placed upon 
the pavement, and traffic is allowed to come upon it. 

In some places these pavements are constructed with- 
out the use of the coal-tar cement, the joints being 
rammed full of sand and gravel ; in other cases the 
blocks are set upon rolled sand and gravel without the 
boards, the blocks being rammed into place ; but other- 
wise the construction is the same as above. 

The method of construction advisable for any partic- 
ular work depends always upon the local conditions 
and requirements. To make a good wood pavement 
there is necessary a solid foundation, blocks of good 
material, and impervious joints, and all such work should 
be so constructed as to secure these conditions in so far 
as available resources will admit. Weak construction 
always involves high cost for maintenance, and greater 
expense in the end than good construction. 

Art. 66. Preservatiois of Wood. 

The most serious objection commonly raised to the 
use of wood pavements is that wood, being porous, ab- 
sorbs moisture readily, and is thus both liable to de- 
struction through decay and to become injurious to 
health. Various methods have therefore been pro- 
posed for rendering the blocks less pervious and more 
durable by impregnating them with various solutions 
which shall fill the pores and act as preservatives. 

The methods which have been principally used are 
known as Burnettizing^ Kyanizing, and Creosoting. 



l8o A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Burnettizing consists in immersing the wood in a 
solution of chloride of zinc until the pores are filled 
with the solution. This is either done by simply im- 
mersing and allowing the wood to gradually absorb the 
solution, or by forcing the solution into the pores of 
the wood under pressure. The first method requires 
considerable time : about two days' immersion to each 
inch of thickness is usually allowed in order to admit of 
the wood becoming saturated with the solution. 

In kyanizing a saturated solution of corosive sub- 
limate is used, and the timber immersed in the solution 
long enough for the pores to become well filled. 

Creosoting consists in impregnating the wood with 
the oil of tar or creosote. In this process the wood is 
first thoroughly dried, usually by heating it in a kiln, and 
the hot creosote is then forced in under pressure. The 
method of accomplishing this varies in different places. 
In order to be effective the process must be thoroughly 
carried out and the pores well filled. It is commonly 
recommended that from 8 to 12 pounds of creosote 
per cubic foot of timber should be forced in, as a mini- 
mum requirement for the softer woods, such as are com- 
monly used in pavements. Creosote has the property 
of destroying the lower forms of animal life, and is 
therefore an effective preservative against destruction 
through these agencies where they exist. This method 
is therefore often employed for the preservation of 
timber for subaqueous construction in sea-water. 

All of the above processes, when properly applied, 
are effective in preventing decay, and therefore in 
lengthening the natural life of the wood. They also 
render the wood practically impermeable, and thus re- 
move the objection to the pavement based upon its 



WOOD PAVEMENTS. l8l 

absorbent nature. They do not, in general, appear to 
increase the resistance of the wood to the wear of the 
traffic, and in most cases the advantage to be gained 
seems so small as to render their economic value for 
this purpose at least doubtful. 

The economic advantage of using treated blocks is a 
question of the relative costs of increasing the expense 
of construction by using them or of the additional ex- 
pense of more frequent renewals where they would be 
necessary without the treatment. The desirability of 
the treatment in any particular instance depends to 
some extent upon the traffic to which the pavement is 
to be subjected as well as upon the character of the 
material available for the purpose. Where the traffic 
is such as to bring a considerable wear upon the pave- 
ment, and sound, well-seasoned blocks are to be had, 
there is usually little, if any, advantage in the treated 
blocks, as the pavement will ultimately fail by the wear 
of the blocks in either case. Experience has shown 
that in many cases the untreated wood wears out in 
the pavement before decay sets in, and that the appli- 
cation of the preservative processes would not prolong 
the life of the pavement. This has been the result of 
experience in London, where after trying many differ- 
ent methods the consensus of opinion is against the 
use of preservative processes. It is claimed, however, 
by some authorities that creosoted blocks have been 
shown in some instances to give greater resistance to 
wear than untreated blocks under the same traffic (see 
London Engineering iox July 29, 1892). This London 
traffic is heavy, the material well selected, and the 
wear severe. There may frequently be cases, however, 
wherewith lighter traffic or with wood of a less durable 



1 82 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

nature or less well seasoned the application of preser- 
vatives may effect such a lengthening of the life of the 
pavement as to make their application economically 
desirable. 

In the treatment of the wood it is essential that the 
process be very thoroughly applied in order to get 
good results. The process most commonly recom- 
mended is creosoting, and in order to derive any bene- 
fit from the treatment it is necessary that the pores of 
the wood be thoroughly filled with the oil. Merely 
dipping the blocks in creosote or tar, as is sometimes 
done, is more likely to be an injury than a benefit, and 
has been found in some cases to be the cause of decay 
by closing the pores upon the surface of the block 
and inducing an internal dry-rot. It is also essential 
to success with creosote that the blocks be thoroughly 
dried before injecting the creosote. 

Art. 6^. Maintenance of Wood Pavements. 

The ordinary maintenance of wood pavements, like 
that of most other pavements, consists in keeping the 
pavement clean and in repairing from time to time any 
small breaks that may appear in the surface due to im- 
perfect material or to the settling of the foundation. 
These repairs would, of course, include the removal of 
any defective blocks and the taking up and replacing of 
any portion which may settle out of surface through 
inefificient support. 

It is generally agreed that the wear of a wood surface 
is improved by giving it an occasional coating of small 
gravel, in some cases two or three times a year, and 
permitting it to be ground into the surface for a few 



WOOD PAVEMENTS. 1 83 

days. It is an advantage also that the surface be kept 
sprinkled in warm weather. 

When the wood pavement needs renewal or exten- 
sive repairs the surface may be relaid as with any other 
block pavement: if a permanent foundation be em- 
ployed, by stripping the blocks from the foundation 
and placing a new surface in the same manner as the 
first one ; with a board foundation that also must be 
relaid. 

If the pavement is cut through for any cause the 
surface may be replaced with the same facility as other 
block pavements; but where a board foundation is 
used it is necessary to use care in replacing in order to 
secure proper bond with the remainder of the founda- 
tion and prevent any subsequent settlement at the 
line of cut. In such cases it is also necessary to com- 
pact the earth very carefully in replacing it, that there 
may be no subsequent settlement. 

The cost of keeping a wood pavement in order, as 
with any other pavement, depends upon the character 
of the work done in construction, — the better the pave- 
ment the cheaper the maintenance. 

Art. 68. Healthfulness of Wood Pavements. 

The use of wood pavement is very often objected to 
upon the ground that it is unhealthful and likely to 
give rise to disease. This is based upon the fact that 
the material of the pavement, being porous and ab- 
sorptive of moisture, is likely to become saturated with 
organic matter from the foul liquids of the surface 
soaking through it. This foul matter must also, on 
account of the permeable nature of the material, pass 



184 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

to some extent through the pavement and contami- 
nate the foundation and soil beneath as well, especially 
where the foundation is a permeable one, as in the case 
of boards or sand and gravel. In addition to the 
danger due to the permeability of the wood, unhealth- 
fulness may also be caused by the liability to decay 
of the material. 

There is much difference of opinion among authon 
ities concerning the extent of the danger to health 
offered by ordinary wood-block pavements, some re. 
garding the danger as a very serious one and protest 
ing against the use of wood in any case, while others, 
although admitting the permeability and perishable 
nature* of the material, consider its proper use quite a 
safe one and the danger as somewhat visionary. Health 
statistics of cities using wood pavements to a large 
extent, compared with those of cities not using them, do 
not indicate anything unfavorable to them ; but it may 
properly be Said that such statistics can seldom be 
compared in such a manner as to give a reliable index, 
as there are so many other circumstances which may 
affect public health, and the conditions other than the 
pavements are rarely the same. 

The likelihood of a pavement producing unsanitary 
conditions depends very largely upon climatic and local 
conditions and upon the construction of the pavement. 
The opinions of those observing the matter are there- 
fore usually based upon their own local surroundings. 
Instances are recorded where blocks of wood after con- 
siderable service in pavements have been found to be 
but little, if any, affected by the absorption of the street 
refuse, and the foundations to be quite unaffected by it ; 
and in other instances blocks have been found to be 



WOOD PAVEMENTS. 1 85 

considerably contaminated, and the foundations and 
subsoil saturated with filth. In most cases these differ- 
ences may be attributed to differences in methods of 
construction as well as in material used, and the cause 
of subsoil contamination appears usually to be open- 
joint construction rather than permeable blocks. 

Where good drainage exists and a pavement is con- 
structed of sound, well-seasoned blocks with close, im- 
pervious joints, so that it cannot get wet at the base, 
the danger from saturation and decay is probably 
small, and on the score of health such a pavement is 
much to be preferred to a stone-block pavement with 
open joints. Under the reverse of these conditions a 
wood pavement may be a serious menace to health. 

In close, damp places, or climates giving the same 
conditions, the liability to decay is much greater than 
where the pavement is exposed to the sun and air. 



CHAPTER X. 
STONE-BLOCK PAVEMENTS. 

Art. 69. Stone for Pavements. 

Stone-BLOCK pavements are commonly employed 
where the traffic is heavy and a material needed which 
will resist well under wear. 

Stone for this purpose must possess sufficient hard- 
ness to resist the abrasive action of wheels. It must 
be tough, in order that it may not be broken by shocks. 
It should be impervious to moisture and capable of 
resisting the destructive agencies of the atmosphere 
and of weather changes. 

Experience only can determine the availability of 
any particular stone for this use. The stone may be 
tested in the same manner as brick,' and perhaps some- 
thing predicated as to the probability of its wearing 
well under traffic ; but the conditions of the use of the 
material in the pavement are quite different from those 
under which it may be tested, and any tests looking to 
a determination of its weathering properties are apt to 
be misleading. 

Examination of a stone as to its structure, the close- 
ness of grain, homogeneity, etc., may assist in forming 
an idea of its nature and value for wear. Observations 
of any surfaces which may have been exposed for a 
considerable time to the weather, either in structures 

186 



STONE-BLOCK PAVEMENTS. if! 



or in the quarry, will be the most efficient method of 
forming an opinion concerning the weathering proper- 
ties of the stone. The conditions of use in pavements 
are, however, somewhat different from ordinary expos- 
ure in structures, on account of the material in the 
pavement being subject to the action of w^ater contain- 
ing acids and organic substances due to excreted and 
refuse matter. A low degree of permeability usually 
indicates that a material will not be greatly affected by 
these influences and also that the effect of frost will 
not be great. 

Granite and sandstones are commonly employed for 
paving blocks and furnish the best material. Lime- 
stones are sometimes used, but have seldom been found 
satisfactory. Trap-rock and the harder granites, while 
answering well the requirements as to durability and 
resistance to wear, are objectionable on account of 
their tendency to wear smooth and become slippery 
and dangerous to horses. Granite or syenite of a tough 
homogeneous nature is probably the best material for 
the construction of a durable pavement for heavy 
traffic. Granites of a quartzy nature are usually brittle 
and do not resist well under the blows of horses' feet or 
the impact of vehicles on a rough surface. Those con- 
taining a high percentage of felspar are likely to be 
affected by atmospheric agencies, while those in which 
mica predominates wear rapidly on account of their 
laminated structure. 

Sandstones of a close-grained compact nature often 
give very satisfactory results under heavy wear. They 
are less hard than granite and wear more rapidly, but 
do not become so smooth and slippery, and commonly 
form a pavement that is more satisfactory from the 



1 88 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

point of view of the user. Sandstones differ very 
widely in character, their value depending chiefly upon 
the nature of the cementing material which holds them 
together. In order that a stone may wear well and 
evenly in a pavement it is desirable that it be fine- 
grained, dense, and homogeneous, as well as cemented 
by a material which is not brittle and is nearly imper- 
vious to moisture. Those sandstones in which the 
cementing material is of an argillaceous or calcareous 
nature are apt to be perishable when exposed to the 
weather. The Medina sandstones of Western New 
York and Ohio have been quite extensively used for 
paving purposes and prove a very satisfactory material 
for such use. 

Limestone has not usually been successful in use for 
the construction of block pavements on account of its 
lack of durability against atmospheric influences. The 
action of frost commonly causes weakness and shiver- 
ing, which produces uneven and destructive wear under 
traffic. There are, however, as wide variations in the 
characteristics of limestones as in those of sandstones, 
and there may be possible exceptions to the rule that 
in general limestone is not a desirable material for 
block pavement 

Art. 70. Cobblestone Pavements. 

Cobblestones have in the past been quite extensively 
used in the construction of street pavements, although 
at the present time they have been for the most part 
abandoned, excepting where they are used at the sides 
of other pavements for gutter construction or some- 
times between the rails of a horse-car track. This 



STONE-BLOCK PAVEMENTS. 1S9 

pavement as ordinarily constructed is a cheap one in 
first cost, and it affords a good foothold for horses. It 
is not usually a durable pavement as the stones are 
easily loosened from their positions, although the 
stones themselves may be practically indestructible 
and used again and again in reconstructing the surface. 

Cobblestone pavements as commonly constructed 
are also objectionable because they are permeable to 
water and difficult to clean. They therefore collect 
and become saturated with the filth of the street 
and are very liable to injury from frost. They are 
also extremely rough and unsatisfactory in use for 
travel. 

For paving the side-gutters, where broken-stone or 
sometimes where wood is used for the travelled portion 
of the street, cobblestones may often be convenient 
and useful, and form a cheap and satisfactory means of 
disposing of surface drainage. Such an arrangement 
is shown in Fig. 31 (p. 186). 

Cobble pavements may also sometimes be advanta- 
geously used upon steep grades where traffic is neces- 
sarily slow and the foothold afforded becomes a very 
important matter. When used for this purpose a con- 
crete foundation should be employed and the stones 
be firmly bedded to prevent displacement through the 
efforts of horses to obtain foothold. 

Cobblestones as used for pavements are usually 
rounded pebbles from 3 to 8 inches in diameter. They 
are set on end in a layer of sand or gravel, rammed into 
place until firmly held in position, and then covered 
with sand or fine gravel and left to the action of travel, 
which soon works the upper layer of sand into the in- 
terstices between the stones. 



190 a t£;xt-book on roads and pavements. 

Art. 71. Belgian Blocks. 

Belgian block is the name commonly applied to a 
pavement formed of nearly cubical blocks of hard rock. 
In the vicinity of New York this pavement has been 
largely used, the material being trap-rock from the 
valley of the lower Hudson. The blocks are usually 
from 5 to 7 inches upon the edges, with nearly parallel 
faces, and as commonly laid are placed upon a founda- 
tion layer of sand or gravel about 6 inches thick. This 
shape of block is objectionable on account of the width 
between joints being too great to afford good foothold 
to horses. The materials of which Belgian blocks have 
ordinarily been formed are very hard and (as already 
noted in Art. 69) wear smooth in service, becoming 
slippery and thus increasing the effect of the too wide 
block. It is also better to have the length of the 
blocks somewhat greater across the street and let 
them break joints in that direction in order that they 
may give greater resistance to displacement under pass- 
ing wheel-loads. 

The older pavements of this character were usually 
placed upon a sand foundation. More recently, this 
practice has, in the better class of work, been super- 
seded by a more solid construction, a concrete base 
being used. 

Art. 72. Granite and Sandstone Blocks. 

For the construction of the better class of stone- 
block pavements, blocks of tough granite or sandstone 
are used, set, in the best work, upon a concrete base, 
although sometimes placed upon a foundation of sand 
or gravel. 



STONE-BLOCK PAVEMENTS. IQI 

These pavements when well constructed are about 
the most satisfactory means yet devised for providing 
for very heavy traffic, as they present a maximum 
resistance to wear with a fairly good foothold for 
horses, and are much more agreeable in service than the 
old form of rough pavements. There is still much to 
be desired in the attainment of smoothness and ab- 
sence of noise, and, as a general thing, it may be said 
that pavements of this kind are desirable only where 
the weight of traffic is so great that the smoother pave- 
ments would not ofTer sufficient resistance to wear. 
Even in such cases it may frequently be questionable 
whether an additional expense for maintaining a pave- 
ment which would be more pleasant in use and less 
objectionable to occupants of adjoining premises 
would not be advisable from an economical as well as 
from an aesthetic point of view. 

Blocks for stone pavements, in the best work, are cut 
in the form of parallelopipeds, 9 to 12 inches long, 3 
inches wide, and 6 or 7 inches deep. The length should 
be sufficient to permit the blocks to break joints across 
the street. The width should be less than that of a 
horse's hoof in order that the joints in the direction of 
travel may be close enough together to prevent a horse 
from slipping in getting a foothold. The depth should 
be sufficient to give a bearing surface in the joints 
large enough to prevent the blocks from tipping when 
the load comes upon one end of it. 

Art. 73. Construction of Stone-block 
Pavements. 

Stone-block pavement for durable and effective 
service should be placed upon very firm foundations. 



192 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Bases of concrete are usually employed and give the 
best results. These foundations are formed as de- 
scribed in Art. 47, and consist of a layer of concrete 4 to 
8 inches thick, 6 inches being the most common depth. 

In constructing the pavement, a cushion coat of sand, 
usually about an inch thick, is spread upon the base of 
concrete, for the purpose of allowing the bases of the 
paving blocl^s to be firmly bedded when the tops are 
brought to an even surface, the sand readily adjusting 
itself so as to fill all the spaces beneath the blocks and 
to offer a uniform resistance to downward motion in 
every part of the pavement, and in like manner trans- 
mitting the loads which come upon the pavement to 
the foundation so as to evenly distribute them over the 
surface of the concrete. The sand used for this pur- 
pose should be clean and dry, and all large particles 
sifted out, as they may prevent the blocks adjusting 
themselves properly. A thin layer of asphaltic cement 
is sometimes used in place of the sand with very good 
results. 

The blocks should be laid as close together as possi- 
ble in order to make the joints small. They are laid, 
like brick, with the longest dimension across the street, 
and arranged in courses transverse to the street, with 
the stone in consecutive courses breaking joints. In 
laying, it is considered best to begin the courses at the 
gutters and work toward the middle, the crown-stone 
being required to fit in tight. 

After the blocks are placed they are well rammed to 
a firm unyielding bearing and an even surface. Stones 
that sink too low under the ramming must be taken 
out and raised by putting more sand underneath. 

As in the case of other block pavements, those of 



STONE-BLOCK PAVEMENTS. 193 

Stone should be made as impervious to moisture as 
possible. The foundation should be kept dry and 
moisture prevented from penetrating beneath the 
blocks, where it has a tendency to cause unequal settle- 
ment under loads, or disruptions under the action of 
frost. In the better class of work, therefore, the joints 
are filled with an impervious material which cements 
the blocks together. Coal-tar paving cement is com- 
monly employed for this purpose, as with brick and 
wood, and seems the most satisfactory in use, although 
hydraulic cement mortar is sometimes used. The coal- 
tar cement is commonly made by mixing coal-tar pitch 
with gas-tar and oil of creosote, a proportion sometimes 
employed being loo pounds pitch, 4 galls, tar, and i 
gall, creosote. 

The use of cement between the blocks binds them 
together and increases the strength of the pavement as 
well as the resistance of the blocks to being forced out 
of surface. It also deadens to some extent the noise 
from the passing of vehicles where asphaltic or coal-tar 
cement is used. 

The method of filling the joints is usually to first 
fill them about one third full of small gravel, then 
pour in the paving cement until it stands above the 
gravel ; then another third full of gravel, more cement 
as before ; then gravel to a little below the top, and the 
joint filled full of cement ; after which a coating of 
fine gravel is distributed over the surface. 

Various modifications of the method above outlined 
are used in the principal cities for a pavement to with- 
stand heaviest traffic and secure a maximum of dura- 
bility : essentially it represents the best modern practice. 

A cheaper form of stone-block pavement is made by 



194 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

laying the blocks directly upon a foundation of gravel 
or sand, either with cemented joints or with joints filled 
with gravel only. This gives a fairly good pavement 
for streets of moderate traffic, and has been extensively 
used in the past. The present tendency, however, 
which will probably increase in the future, is to lessen the 
use of pavements of this character, and to substitute a 
surface which is more pleasant in use for all service 
where durability and resistance to wear are not the 
prime requisites. 

Art. 74. Stone Trackways. 

In some of the European cities, particularly in Italy, 
stone trackways are sometimes employed on streets of 
heavy traffic for the purpose of diminishing traction. 
These trackways are formed of smooth blocks of stone 
4 to 6 feet long, 18 to 24 inches wide, and 6 to 8 inches 
deep, laid flat and end to end so as to form a smooth 
surface upon which wheels may move with the least 
possible resistance. Between the tracks, and usually 
the remainder of the street, is commonly paved with 
cobble. The method of construction is shown in Fig. 
25. The tracks drain to the middle, and the pavement 




Fig. 25. 



between is made concave and provided with openings 
into the storm sewers for the escape of surface-water. 
The track and pavement are laid upon a layer of sand 
resting upon a broken-stone or gravel foundation. 



STONE-BLOCK PAVEMENTS. 1 95 

Such trackways are very durable under heavy traffic, 
and give very light traction combined with good foot- 
hold. It is possible that they might advantageously 
be applied oftener than they are on streets used for 
heavy hauling. 



CHAPTER XL 
CITY STREETS. 

Art. 75. Arrangement of City Streets. 

The location of streets should be planned with a 
view to giving direct and easy communication between 
all parts of a city. The arrangement should also be 
such as to permit the subdivision of the area traversed 
by them in such a manner as to give the maximum of 
efficiency for business or residential purposes. The 
most obvious and satisfactory method of accomplishing 
these purposes is usually by the use of the rectangular 
system, with occasional diagonal streets along lines 
likely to be in the direction of considerable travel. 

Streets so far as possible should be systematically 
arranged and continuous throughout the extent of the 
city, both to facilitate travel and to admit of their being 
so named and numbered that the locality of a place 
of business or residence may at once be evident, from 
its address, to any one familiar with the general plan 
of the city. The rectangular system is desirable on 
this account, and also because it furnishes blocks of the 
best form for subdivision into building lots. 

The proper arrangement of streets will always neces- 
sarily depend in some measure upon the natural feat- 
ures of the locality, and any system of arrangement 
will be more or less modified by local topography. 

196 



CITY STREETS. 1 9/ 

Where for topographic or aesthetic reasons it may be 
considered desirable to use curved b'nes for the streets, 
the continuity and uniformity of arrangement should 
be maintained as far as possible. The use of curves 
on residence streets may sometimes be advantageous 
in reducing gradients or in its effect upon adjoining 
property through avoiding heavy earthwork. Where 
a change in direction is necessary the use of a curve 
usually gives a better appearance than an abrupt bend, 
unless the change can be effected at the intersection of 
a cross-street. Care is required, however, to prevent 
the local introduction of curvature disarranging the 
general plans and producing the chaotic condition due 
to an irregular use of short streets. 

In laying out a rectangular system of streets the 
blocks ordinarily \yill preferably be long and narrow. 
The distance needed between streets in one direction 
is only that necessary to the proper depth of lots, while 
in the other direction the streets need only be close 
enough to provide convenient communication for the 
travel and trafific. A convenient method would be to 
lay out the main streets so as to form squares large 
enough to permit the introduction of an intermediate 
minor street through the blocks. These minor streets 
may then be introduced in the direction that seems 
advisable in each locality. Such an arrangement is 
shown in Fig. 26. The diagonal streets cut more space 
from the blocks traversed by them, but give more 
frontage, and property fronting them will usually have 
more value than other property in its vicinity. 

The proper location for diagonal streets intended as 
thoroughfares for traffic is naturally determined by the 
positions of the business centres or public buildings 



198 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

and parks, from which they may radiate in such manner 
as to bring the outlying portions of the city into the 
most direct communication possible. 

A city cannot usually be laid out complete. Its for- 
mation is a matter of gradual growth and enlargement, 















/ 


^A 






V 


























//I 












/ / 


^ 




V 
























VA 



















Fig. 26. 



and the end cannot be seen from the beginning. For 
this reason it is frequently necessary to undergo great 
expense in the larger cities in cutting new streets or in 
changing the positions or dimensions of existing old 
ones in built-up districts in order to relieve the 
crowded condition of the streets, which hampers busi- 
ness and renders travel difficult and unpleasant. Much 
of this difficulty might frequently be obviated if in 
growing towns and cities proper attention were given 
to the regulation of suburban development. Such de- 
velopment should be under municipal control so far 
as to require at least that each new subdivision which 
opens new streets should be made with a view to 
affording proper ways of communication between ad- 
joining properties by making streets continuous. 
Where such regulation does not exist streets will be 




t^m^ 






Fig. 27. 



^n 



200 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



laid in any naanner to best develop the particular prop- 
erty in which they are placed. 

A good example of the advantages of systematic and 
liberal plans in street arrangement, as well as of the 
evils of unregulated extension, is given by the case of 
Washington, D. C. 

Fig. 27 shows a portion of the city of Washington 
illustrating its systematic arrangement. It consists of 
a rectangular system, together with two sets of diag- 
onal avenues, and open squares or circles at the inter- 
sections of the avenues. 

Fig. 28 shows a number of suburban subdivisions on 
the borders of the city of Washington, made previous 
to the adoption of the law regulating them. In some 




rx 



a»flH^ 



n 






Fig. 28. 



cases the streets of adjoining subdivisions have no 
communication with each other, and the general ten- 
dency is toward a labyrinth of short streets. The law 
now requires that all street extension within the Dis- 



CITY STREETS. 20 I 

trict of Columbia shall conform to the general plan of 
the city of Washington ; and under the operation of 
this law the lines of many of the city streets have been 
extended to all parts of the District, and all of the 
suburban development is being gradually brought with 
the city into one harmonious whole, on the same gen- 
erous plan that exists within the city. The rectification 
of the irregular plats upon the borders of the city must, 
however, be a matter of heavy expense to the District. 

Art. ^(i. Width and Cross-section. 

The width of city streets is important both on ac- 
count of its influence upon the ease with which traffic 
may be conducted, and because of its effect upon the 
health and comfort of the people, by determining the 
amount of light and air which may penetrate into 
thickly built-up districts. 

To properly accommodate the traffic of commercial 
thoroughfares in business districts of towns of consider- 
able size, a street should have a width of lOO to i6o 
feet, the whole of it to be used for roadway and side- 
walks. Wide streets are especially needed where, as in 
the larger cities, they are bordered by high buildings 
or are to carry lines of street railway. 

Residence streets in a town of considerable size, 
where houses are set out to the property line and stand 
close together, should have a width of at least 80 to 100 
feet in order to look well and give plenty of light and 
air. 

The streets in nearly all large towns are laid out too 
narrow ; they are crowded and dingy. The chief diffi- 
culty is that the future of a street is not usually fore- 



202 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

seen when it is located. Owners in subdividing prop- 
erty are only anxious to get as many lots as possible 
out of it, and there are usually no regulations looking 
to the future health and comfort of resident when the 
street shall be built upon. In the growth of a town the 
nature of localities change : residence streets become 
business streets, streets devoted to retail trade become 
wholesale streets, and mercantile districts are given up 
to manufacturing. If a city could be laid out com- 
plete from the beginning it would be comparatively 
easy to consider the requirements to be met and locate 
the streets accordingly. Under existing conditions 
this is not possible, but a more liberal policy in planning 
streets would usually be found of advantage in any 
growth that may ensue. There is also very frequently 
an immediate financial advantage in the enhancement 
of values due to wide streets. A lot lOO feet deep on 
a street 8o feet wide will nearly always be of greater 
value than if the same lot be i lO feet deep and the 
street only 60 feet in width. 

In Washington, D. C, which probably has the best 
general system of any American city, no new street can 
be located less than 90 feet in width, and avenues 
must be at least 120 feet wide. Intermediate streets, 
called places, 60 feet wide, are allowed within blocks, 
but full-width streets must be located not more than 
600 feet apart. The value of this liberal policy to the 
city of Washington is evident not only in the increased 
comfort of the people, but in its large growth as a resi- 
dential city and the increased value of property in it. 

While it is advantageous to have the street wide be- 
tween building-lines, it is not necessary that the whole 
street width be used for pavements. The street pave- 



CITY STREETS. 203 

ment should be gauged in width by the immediate 
necessities of the traffic which is to pass over it. The 
pavement should be wide enough to easily accommo- 
date the traffic, but any unnecessary width is a tax 
upon the community in the construction and mainte- 
nance of more pavement than should be required, and 
perhaps diminishes the length of street which may be 
improved with available funds. Thus, for a residence 
street in general a width of 30 to 35 feet between 
curbs is usually ample, with a foot-walk upon each side 
6 to 10 feet wide. The remainder of the street width 
should be made into lawns upon each side, with tree 
spaces between the sidewalk and roadway. 

Fig. 29 shows in partial section the arrangement of a 



==^ 



' W///////v///y////'^//^^<^/^/^ 



- - 33.F». -*U.3 ^. -5Pf,; ,<. . L,AWN 17 Fh • • 

Fig. 29. 

90-ft. residence street for moderate traffic. For resi- 
dence streets of lesser importance, where the travel 
is light and the street is only required to furnish 
facilities to meet the needs of its immediate locality, a 
less width of pavement may often be advantageously 
used. A pavement 24 feet wide is sufficient to accom- 
modate a very considerable amount of light driving, 
and in many places, especially in the smaller towns 
where funds for effective improvement are obtained 
with difficulty, even less widths maybe employed with 
the result of improving the streets both in appearance 
and usefulness. All that is really needed in such cases 
is room for teams to pass comfortably and to turn 
without difficulty. The narrowing of roadways on 
streets of light traffic to what is really necessary may 



204 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

often make possible improvements which will turn a 
broad sea of mud into a narrow hard roadway and a 
grass-plat. Fig. 30 shows the arrangement of a village 
street 50 feet wide for light service. 

In many cases for village streets, where the traffic is 
light and it is essential that the cost of construction be 




low, it may be good practice to construct the travelled 
portion of the roadway of macadam, wood, or other 
pavement, and use cobble gutters at the sides without 
curbs. Fig. 31 shows a roadway 30 feet wide, with 
macadam middle and cobble gutters. In Saginaw, 
Mich., this method has been followed, using either 
macadam or wood blocks for the middle portion, and 




Fig. 31. 



in the report of City Engineer Roberts for 1893 it is 
recommended as economical and efficient. 

The cross-section of streets must be arranged with 
reference to proper surface drainage. The street is 
given a crown at the middle to throw the water into 
the gutters, and sidewalks usually have a sufficient in- 
clination toward the gutter to cause them to drain over 
the curb. The section necessary for street drainage is 
discussed in Art. 10. The street is usually made prac- 
tically level across, the curbs and sidewalks at the two 
sides being given the same elevation. The parking at 



CITY STREETS. 20$ 

the sides may have a slope between the sidewalk and 
the building-line when it is necessary or advantageous. 
Sometimes, on streets along a slope, expense may be 
saved or adjoining property benefited by placing the 

w ■ ' - (I ' ' ■ < I . ■ ■ ■ . .jj . - ^ 

Fig. 32. 

sidewalk at a different elevation from that of the street, 
as shown in Fig. 5, or by placing one curb lower than 
the other and moving the crown of the road to one 
side, as shown in Fig. 32. 

Art. 77. Street Grades. 

The grades of city streets necessarily depend mainly 
upon the topography of the site. Wherever possible, 
it is desirable that grades be uniform between cross- 
streets. 

In establishing grades for new streets through unim- 
proved property, they may usually be laid with refer- 
ence only to obtaining the most desirable gradients for 
the street within a proper limit of cost. But where 
improvements have already been made, and located 
with reference to the natural surface of the ground, it 
is frequently a matter of extreme difficulty to give a 
desirable grade to the streets without injury to adjoin- 
ing properties. In such cases it becomes a question of 
how far individual interests shall be sacrificed to the 
general good. It may be said in this connection that 
adjustments to new grades are usually accomplished 
much more easily than would be anticipated, and when 
accomplished the possession of a desirable grade is of 



2o6 A TEXT-BOOIC ON ROADS AND PAVEMENTS. 

very considerable value to adjoining property. Too 
great timidity should not, therefore, be felt in regard 
to making necessary changes because of the fear o-f in- 
juring property in the locality. 

Where a grade if made continuous between inter- 
secting streets would be nearly level, it is frequently 
necessary to put a summit in the middle of the block 
and give a light gradient downward in each direction 
to the cross-streets in order to provide for surface 
drainage. The amount of slope necessary to provide 
for proper drainage depends upon the character of the 
surface and smoothness of the gutter. For a surface 
of earth or macadam the slope should not be less than 
about I in loo, and for paved streets from i in 200 to 
I in 250. 

In some cases it may be possible to give sufficient 
slope to gutters to carry off the surface-water by mak- 
ing the gutter deeper at the ends than in the middle of 
the block without making a summit in the crown of 
the street. The curb in such case would be made 
level or of uniform gradient. 

It may frequently be necessary to consider the 
effect of grade in determining the character of pave- 
ment to be employed upon a street. Asphalt is com- 
monly limited to grades of 4 or 5 per cent, although 
some engineers use it on 6 or 7 per cent grades. Brick 
is commonly used on grades up to about 8 per cent, 
and in some places has given satisfactory service on 10 
per cent grades. Wide joints, about i inch, are some- 
times used in brick pavements on steep streets, in order 
to afford a better foothold for horses. This, however, 
in other instances appears to be unnecessary, provided 
the pavement is kept clean and in good condition. 

Wood blocks may safely be used on grades of 6 or 



CITY STREETS. 207 

8 per cent, while smooth stone blocks are employed in 
about the same manner as bricks, being if anything a 
little more slippery than bricks. Stone blocks of some- 
what rough character are successfully used in some in- 
stances on grades of 12 or 13 per cent. 

In a report on the streets of Duluth in 1890, Messrs. 
Rudolph Hering and Andrew Rosewater recommend 
for steep streets, in addition to the above, that brick 
may be used in which the tops are rounded, and that 
wood blocks for such use have their upper edges cham- 
fered on each side, or if round blocks be used, around 
the blocks. Subsequent experience has, however, 
seemed to indicate that, except in extreme cases, such 
special construction is not necessary. 

On streets too steep for smooth pavement it is not 
unusual to pave part of the street width with a smooth 
pavement, like asphalt, and the remainder with stone 
blocks or some rough pavement for use in slippery 
weather. 

Art. 78. Street Intersections. 
At intersections the crown of the roadway pavement 
on each street should, if possible, be continuous to the 
centre of intersection, in order to prevent vehicles on 
one street from being subjected to the jar incident to 
passing over the gutter of the other. Where a storm- 
sewer is available into which the water from the gut- 
ters on the upper side can be emptied this is a simple 
matter, but where such sewers do not exist it requires 
the adoption of some special means of draining the 
gutters on the upper side. This may sometimes be 
accomplished by a culvert across the street, the gutters 
being somewhat depressed at the corners to bring the 
channel sufificiently low. In other cases, where the 
slope is sufficient, it is more satisfactory to construct 



2o8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



an underground pipe-drain from the upper corner to 
some point in the gutter below the crossing. 

Where the rate of grade is such that it is feasible, it 
is desirable that the grade of both streets should be 
brought to a level at intersections. The top of the curb 
at the four corners should be at the same elevation, thus 
permitting the continuation of the full section of each 
roadway until they intersect. It is also desirable that 
the sidewalks at the corners be level; that is, the points 
a a in Fig. 33 should all be placed at the same eleva- 



a 



Fig. 33. 

tion, which will make the entire street section, includ- 
ing sidewalks, horizontal across the direction of travel 
on each street. 

On very steep slopes it may not be possible to flatten 
out the grade to a level in crossing transverse streets, 
and in such cases the elevations require study, and need 
to be carefully worked out for each particular case. In 
the report of Messrs. Rudolph Hering and Andrew 
Rosewater upon the streets of Duluth, it is recom- 
mended that in all cases the grade shall be reduced to 
3 per cent between the curb-lines of cross-streets, and ^ 



CITY STREETS. 209 

the grade of the curb reduced in all cases to 8 per cent 
for the width of the sidewalks of intersecting streets. 
This is to be considered the maximum allowable rate 
of transverse grade, and only to be employed in case of 
necessity. If in Fig. 33 the arrow represents the direc- 
tion of steep slope, and the street transverse to that 
direction has a roadway 40 feet wide with sidewalks 
10 feet wide, the above limits would permit the curb 
at c to be 1.2 feet lower than that at ^, and admit of 
a fall of 0.8 foot in the curb line from a \.q b and from 
c to d. If both streets have the same grade and 
wadth the curb at the lowest corner would be 2.4 feet 
lower than at the highest corner. 

Sometimes, where the parallel streets in one direction 
follow the lines of greatest slope, and the cross-street 
are normal to them, the proper grades at intersections 
may be arranged by giving the streets along the slope 
a section similar to that shown in Fig. 32 throughout its 
length, thus permitting the street in the direction of 
slope to continue its grade across the intersection 
without altering at that point the side slope of the 
cross-street. 

For a case of maximum slope this would make the 
section of the roadway of the cross-street a plane sur- 
face sloping uniformly from the upper to the lower 
curb, or in Fig. 32 it would transfer the street crown to 
the upper curb. 

Art. 79. Footways. 

Footways are not required to bear the heavy loads 
which come upon the roadway pavement, but in streets 
of considerable travel are subjected to a continual 



210 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

abrading action, and for good service are required to 
be of a material which will resist abrasion well, of so 
uniform a texture as to wear evenly, and not hard 
enough to become smooth and slippery in use. 

A good sidewalk should always present an even sur- 
face, and therefore requires a firm foundation to resist 
the displacement of the blocks of which it may be com- 
posed. It must also be durable under atmospheric 
changes, and of material that may be easily cleaned. 
The materials commonly employed are gravel, wood, 
brick, tar, asphalt, stone, and artificial stone. 

Gravel walks are the cheapest of footways where 
suitable material is available. They are constructed in 
a manner similar to that used for gravel roadways, and 
require that the bed of the walk be well drained, and 
that it be well compacted by rolling or ramming before 
the walk is placed upon it. The best gravel walks are 
usually built upon a base of rough stone. This base 
may be 6 or 8 inches thick, and forms a solid founda- 
tion upon which the gravel surface may be placed and 
sustained against settling. Walks constructed in this 
manner are frequently used in city parks where the 
travel is considerable. On suburban roads, gravel 
walks usually consist of a thin surface of gravel laid 
upon the earth-bed, and are replaced by some other 
surface when a more expensive construction can be 
afforded. Gutters are frequently necessary to protect 
the walks from the wash of surface-water, which other- 
wise very quickly destroys it. 

Wood is commonly used for walks in the form of 
planks, which are laid on stringers, the planks being 
placed perpendicularly to the direction of travel. It is 
comparatively short-lived, and requires considerable 



CITY STREETS. 2 1 I 

expenditure for repairs, as the material is perishable 
and also wears rapidly. 

Brick footway pavements have been extensively used 
for many years, and form, when well constructed, a very 
durable and satisfactory sidewalk. As commonly con- 
structed they consist of ordinary hard-burned bricks 
laid flat upon a layer of sand over the earth-bed. For 
light travel, pavements so constructed may last well 
and give good service ; but they are apt to soon become 
uneven through the sinking of the bricks because of in- 
sufficient foundation. 

In constructing such a pavement the sand layer 
should be well compacted by rolling or ramming be- 
fore setting the bricks, which should also be rammed 
to a firm and even bearing. To give satisfactory re- 
sults, a foundation of sand and gravel or broken stone 
should be formed 8 or lo inches in thickness. In 
Washington a layer of gravel 4 inches thick and well 
compacted is used, with a layer of sand of the same 
thickness upon it to receive the surface. In forming 
the pavements, the bricks are laid fiat and as close as 
possible. The joints are filled with sand, usually by 
coating the surface with a layer of sand before ram- 
ming, and after completion a second coating, which is 
allowed to remain a few days aftisr admitting the travel 
to it. 

Care must be used in selecting brick for this purpose 
to get only hard-burned brick of uniform quality, 
in order that the resistance to wear may be even. 
The use of vitrified paving brick, as used for roadway 
pavement, would be of advantage on walks subjected 
to heavy wear. 

The use of a concrete foundation and setting the 



212 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

brick on edge and in mortar, after the manner of con- 
structing a roadway pavement, makes a very durable 
sidewalk under heavy traveh It is, however, some- 
what expensive, and usually a stone surface would be 
preferable where such expense is to be incurred. 

Footway pavements of a concrete in which coal-tar 
is the binding material have been widely used, but have 
not usually been satisfactory in use. As commonly 
constructed they wear rapidly and soften, becoming 
very disagreeable in hot weather. Some pavements of 
this character have, however, shown fairly good service. 

Numerous methods have been proposed and tried 
for the construction of tar foot-walks, differing from 
each other in the materials mixed with the tar to form 
the concrete, and in the manipulation of the process. 
Ashes mixed with sand and gravel are usually em- 
ployed, and sometimes clinkers from an iron foundry. 
A somewhat successful pavement of this class has a 
small amount of Portland cement mixed with the ashes 
and sand used in forming the concrete before the addi- 
tion of the tar. 

Asphalt footway pavements are formed either of as- 
phalt blocks or of a surface of sheet asphalt. Wheie 
blocks are used they are laid in the same manner as 
brick upon a foundation of sand or gravel. The 
blocks, or tiles as they are commonly called, are usu- 
ally made flat, about 8 inches square and 2 to 2|- inches 
thick. They are laid with their edges either at right 
angles to the street line or at an angle of 45° with 
the street line, — usually at right angles, on account of 
greater ease in laying. 

Sheet-asphalt footways are laid in the same manner 
as an asphalt street pavement, the pavement, however, 



CITY STREETS. 213 

being given a less thickness. In Washington, D. C, 
these pavements are made about 3 inches thick, and 
constructed upon a bituminous base. Material re- 
moved from street pavements in resurfacing is used for 
forming the surface material of the footway. Mixtures 
of coal-tar and asphalt similar to that used for distillate 
pavement, as noted in Art. 61, are also used in foot- 
ways, and are commonly spoken of as asphalt. 

In the use of rock asphalt for footways, the asphalt 
mastic mentioned in Art. 57 is commonly used, mixed 
with sand or gravel to give a wearing-surface. The in- 
gredients are heated together and applied hot to a 
broken-stone or concrete foundation. In Europe hy- 
draulic cement concrete is used for the base, as in the 
driveways. A layer of 3 or 4 inches of concrete is em- 
ployed, with a surface layer of rock asphalt or asphalt 
mastic and sand, J to f inch in thickness, foj: ordinary 
work. 

Natural stone for foot-walks is ordinarily used in the 
form of flagging. Where flagstones of proper size and 
good wearing qualities may be readily obtained, this 
kind of pavement, if well laid, makes a durable and 
satisfactory foot-walk. Flagstones should be set upon 
a solid foundation and be firmly bedded so as to 
preserve an even surface. They should not be laid, as 
is common in many places, directly upon an earth-bed, 
but should have a cushion layer of sand or of some 
porous material to prevent unequal settling under the 
action of frost. 

Artificial-stone pavements, when well constructed of 
good materials, make the most satisfactory of foot- 
ways. They form an even surface, quite agreeable in 
service, and are durable and economical where exposed 



214 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

to considerable travel. Pavements of this kind are 
either constructed of blocks of material made at a fac- 
tory and carried to the site of the walk, or the stone is 
formed in the position in which it is to be used. The 
latter plan is more commonly followed and admits of 
the use of larger blocks, the size in this case being only 
limited by the necessity of providing for changes of 
dimension with those of temperature, very large blocks 
being liable to crack under such changes. 

There are a number of methods of preparing arti- 
ficial stone for pavements, many of them patented, 
differing to some extent in the composition of the 
material or the details of the work. In general the 
process consists in placing a layer of concrete 4 to 6 
inches thick upon a layer of gravel or other porous 
material. A surface of rich mortar or concrete, com- 
posed of hydraulic cement with sand or crushed 
granite, is given to the pavement, and the surface is 
commonly roughened by scratching lines upon it 
before it is hardened. As with all other concrete- 
work, the pavement needs to be kept damp and pro- 
tected from the sun until the mortar is fully set. A 
layer of damp sand spread over the surface may be 
advantageously employed to protect it for several days 
after it is opened to travel. 

Art. 80. Curbs and Gutters. 

Curbs are usually set in the streets of towns at the 
sides of roadway pavements for the purpose of sus- 
taining and protecting the sidewalk or tree space, and 
of forming the side of the gutter. They are commonly 
formed of natural stone, but sometimes also of artificial 
stone,, clay blocks, or cast iron* 



CITY STREETS, 215 

The curbs used in different places vary considerably 
in form and dimensions. Stone curbs vary from 4 to 
12 inches in width and from 8 to 24 inches in depth. 
They are usually employed from 3 to 6 feet in length, 
and set with close joints. 

The depth must be sufficient to admit of their being 
firmly bedded, and to prevent overturning into the 
gutter. The front of the curb should be hammer- 
dressed to a depth greater than its exposure above the 
gutter, and the back deep enough to permit the side- 
walk pavement to fit close against it where the side- 
walk adjoins the curb. The ends of the blocks should 
also be dressed to the depth of exposure, and the part 
below the ground trimmed off so as to permit the 
dressed ends to come in contact when laid. 

Granite is usually considered the best material for 
curbs, although both sandstones and limestones are 
used in many places. In the vicinity of New York the 
North River bluestone has proved a good material for 
the purpose., 

There are various ways of setting the curb. The 
object should be to bed it firmly on a solid foundation. 
The best method is to place a bed of concrete under it. 
This construction is shown in Fig. 34, which repre- 
sents the method used in setting granite curb in Wash- 
ington, D. C. The curb is held firmly in place by the 
concrete foundation, which joins it rigidly to the road- 
way pavement. 

Where the concrete foundation is not used under 
the curb a deeper curbstone is necessary, usually from 
18 to 24 inches in good work. Curbs are very com- 
monly set in the natural ground, the pavement coming- 
against it on one side ; but it is usually found advau- 



2l6 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

tageous to lay them upon a bed of gravel or broken 
stone, with gravel filled in the trench about them. 




Fig. 34. 

The ordinary method of setting curbs is shown in 

Fig. 35- 

The Washington specifications for ordinary work 
require that a bed of gravel 4 inches deep be used 
under the curb, and that the trench be filled with 




Fig. 35. 



gravel placed in layers 3 or 4 inches deep, each layer 
being thoroughly rammed before adding the next. 
Curbs of artificial stone or concrete are usually 



CITY STREETS. 2 1/ 

formed by mixing the concrete upon the ground and 
placing it in the position it i.^ to occupy, using a board 
mould, as in constructing artificial-stone foot-walks, to 
give it proper shape. By this method of construction 
the curb and gutter may be made practically in 
one piece, where a concrete base is used for the 
pavement. The concrete for the curb and gutter is 
made of smaller materials and with a higher percen- 
tage of cement than in preparing the foundation for 
the roadway, and is given a surface coating of cement 
mortar which is commonly formed of a mixture of Port- 
land cement with finely crushed granite. 

Specifications for artificial-stone curb in Washington, 
D. C, require that the concrete be composed of i 
pajrt Portland cement, 2 parts clean sharp sand, and 
3 parts clean broken stone not more than i inch in 
their largest dimensions. The exposed surface of both 
gutter and curb is to be coated i^ inches thick with a 
mortar composed of 3 parts granulated granite (the 
fragments being of such size as to pass through a 
^-inch screen, and free from dust) and 2 parts cement. 

Artificial-stone curbs are sometimes made hollow, 
and the interior spaces used as a conduit for pipes or 
wires. A variety of forms are used for these cases, 
the curb being usually made in blocks at a factory and 
set like natural stone, the blocks being commonly 
lormed in separate parts which may -be fitted together 
to form the curb and removed to give access to the 
openings. Where the hollow curbs are in one piece, 
hand-holes are placed at short intervals to admit of 
using the openings ; this may be done in case the con- 
duits are to be used for wires. 

Curbs of burned clay or brick are made in several 




2l8 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

forms, both solid and hollow, and are frequently used 
on streets paved with brick, where stone suitable for 
curbing is lacking. 

Cast-iron curbs are sometimes employed, although 
they have not come into use extensively. 
They consist usually of a casting similar to 
that shown in section in Fig. 36, which forms 
the face and top of the curb, being open 
at the back and braced with ribs at short 
Fig ^6 ' ^"^^^^^^^ ^^ length. They are held in place 
by ties attached to the ribs, and the backs 
are filled and tamped to a firm bearing. 

Wrought-iron plates or angles are sometimes used as 
a protection to concrete, or to resurface a worn stone 
curb, the iron being fitted to the face of the curb so as 
to form the exposed surface. Several forms are used, 
and the process is patented. 

Gutters are commonly formed of the same material 
as the roadway pavement, which is simply extended 
to the curb. 

In streets paved with brick or granite blocks the 
gutter blocks are sometimes turned lengthwise of the 
street, as shown in Fig. 22, for the purpose of faciUtat- 
ing the flow of water in the gutter. As already pointed 
out, however, this has the effect of making a continuous 
joint between the pavement and gutter, and its utility 
seems doubtful. 

For streets paved with broken stone it is common to 
employ stone gutters, formed of cobblestones, of narrow 
flags laid lengthwise of the gutter, or sometimes of rec- 
tangular blocks. Such construction is shown in Fig. 35. 
On streets paved with wood these gutters may also be 
frequently employed with advantage, especially where 



CITY STREETS. 219 

for any reason the gutter is likely to be kept damp. 
In forming a cobble gutter the stones are usually set 
upon a layer of sand or gravel after the manner of 
forming a cobble pavement. They should be firmly 
bedded and form an even surface. 

Cobble gutters are often used on village streets 
where no curbs are set, and in such locations where 
but slight expense is admissible they are quite satis- 
factory if properly constructed. This method of con- 
struction is illustrated in Fig. 31. 

Sometimes in work of this kind a flagstone is used 
for the bottom of the gutter and the sides are formed of 
cobble. This is preferable as affording a more free 
channel for the flow of the surface drainage. 

To obtain satisfactory results it is always necessary 
that the foundation be of sufficient depth and well 
compacted, in order to prevent the surface becoming 
uneven by the stones being forced downward into the 
road-bed in wet weather or through the action of frost. 
A layer of 6 to 10 inches of gravel or sand is usually 
required. 

Where flagstones are used to form the gutter, they 
should be 3 or 4 inches thick, 10 to 15 inches wide, as 
may be required, and about 3 feet long. Care is re- 
quired in laying that they may have an even bed and be 
well supported by the foundation. 

Gutters of bricks, or of stone blocks, are often used for 
streets upon which the roadway pavement is asphalt, 
on account of the liability of the asphalt being injured 
by dampness. In this case the gutter is constructed 
by setting the bricks or blocks with their greatest 
length along the street. They are placed upon a bed 
of concrete, the same as is used for the foundation 



220 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

under the asphalt surface, and the joints are filled with 
coal-tar paving cement, as in constructing brick pave- 
ment. 

It is also advisable in using flagstone gutters that 
consecutive blocks should have different widths, differ- 
ing by 2 or 3 inches, in order that there may not be a 
continuous joint between the flagstones and the pave- 
ment of the travelled roadway. 

Art. 8i. Crossings. 

On streets paved with a smooth hard surface which 
is easily cleaned, such as brick or asphalt, special foot- 
way crossings are not usually required or desirable, 
unless the foot travel be very considerable. On other 
pavements, however, which are apt to be rough to 
walk upon or muddy in bad weather, as upon stone, 
wood, or macadam, footways of flagstones are com- 
monly provided, and form the most satisfactory 
crossing. 

These crossings consist of flagstones about lo or 12 
inches wide laid in rows across the street, the rows 
being 6 or 8 inches apart and paved between with stone 
blocks set in the ordinary manner. The crossing- 
stones are 3 or 4 feet long, and at least 6 inches 
thick in order that they may not be broken by the 
traffic. They should be laid with close joints and 
firmly bedded upon the foundation. 

At street intersections where the number of pedes- 
trians is large it is desirable that the crossing be 
carried across on the level of the top of the curb 
without leaving a step at the gutter crossing. This 
may be accomplished by bridging over the gutter with 



CITY STREETS. 2:^1 

a flagstone or iron plate, or by placing the outlets for 
surface drainage a few feet back from the corner and 
eliminating the gutter at the corner. 

Art. 82. Street-railway Track. 

Track for street railways upon paved streets should 
be constructed with a view to offering as little obstruc- 
tion to ordinary street traffic as possible, while per- 
mitting the ready operation of the railway. These 
two points are apt to conflict, and the interest of the 
railway company in the construction of track is rarely 
identical with that of the public use of the street. 

Any street-car track is objectionable on a paved 
street, both on account of the increased wear caused 
to the pavement, and because it forms an obstruction 
to the ordinary traffic of the street. It is, however, 
a necessary evil, being required for the convenience 
of the public, and its detrimental effects may often be 
greatly lessened by proper attention to the methods 
of construction employed. On smooth pavements 
properly constructed track should offer no obstruction 
to vehicles crossing it, and afford no channels in 
which the wheels of vehicles may run and which pre- 
vent wheels readily leaving the track. 

This requires that the surface of the pavement be 
flush with the top of the rail, and that it be laid in 
close contact with the rail. 

It is also important that the method of construction 
used in both track and pavement be firm and substan- 
tial to prevent unevenness due to the yielding of the 
track or settlement of the pavement. 

Construction of Track. — Methods of construction 
used for street-railway tracks are extremely various, 



222 A TEXT-BOOK ON ROADS AND PAVEMENTS. 



and opinions differ widely concerning them. When 
the traffic of the railway and street are light it is gen- 
erally conceded that the most economical method is 
that of placing the rails directly upon wooden cross- 
ties, as in the construction of steam roads. Where, 
however, the traffic is heavy the difficulty and ex- 
pense of making repairs becomes great, and the rail- 
way companies commonly recognize the advantage of 
solid and permanent construction. Several methods 
have therefore been devised for securing firm support 
to the rails. 

Fig* 37 shows the ordinary method of construction 
where a concrete base is employed for the pavement 




Fig. 37. 

and the tie is embedded in the concrete. In this«con- 
struction the track is surfaced up by ballasting in the 
usual manner under the ties with gravel or broken 
stone, after which the concrete base is filled in between 
and perhaps over the ties. The depth of rail is some- 
times made the same as the thickness of the upper 
layers of pavement, thus bringing the top of the tie 
even with the surface of the concrete. Thus a six- 
inch rail may be used with a^brick pavement having 
a two-inch sand cushion as shown in Fig. 38. If the 
depth of rail be less than this, stringers, as in Fig. 39, 
or chairs, as in Fig. 40, are necessary to raise the rails 



CITY STREETS. 



223 



to the level of the paving surface. When stringers 
are employed they are usually connected by cast-iron 




Fig. 38. 

braces to the cross- ties, and are also bedded and held 
in place by the concrete base of the pavement. The 
ties in such case are usually below the concrete. To 




Fig. 39. 




Fig. 40. 

secure greater stability when the rails are supported 
by cross-ties a bed of concrete is sometimes placed 
under each tie and the track is tamped in concrete. 



224 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

This is shown in Figs. 38 and 40. In such construc- 
tion it is usual to make a trench under the tie, fill this 
with concrete and tamp the tie with concrete, after- 
ward placing the concrete base for the pavement be- 
tween the ties. 

On important lines in streets of heavy trafific re- 
pairs to track are often both difficult and expensive, 
and very rigid and substantial construction is essential 
to an economical operation of the railway. To secure 
such construction the wooden ties are sometimes dis- 
pensed with and the rails placed directly upon the 
concrete. Several methods of construction of this 
character have been employed. Fig. 41 shows the 




Fig. 41. 

simplest form where the rails are placed directly upon 
the concrete base of the pavement and spaced by iron 
tie-rods at intervals of six or eight feet. The con- 
crete in this construction is usually made extra heavy 
in order to adequately support the rails and maintain 
them at the level of the pavement. 

A more economical method of securing permanent 
construction is by the use of a concrete beam or 
stringer under the rail. This method of construction 
is illustrated in Fig. 41a. The concrete stringers are 
usually made of Portland-cement concrete from 9 to 
12 inches in depth and 12 to 18 inches in width. The 
rails are commonly held in place by iron ties to which 
the base of the rail is bolted, as shown in figure. Fre- 
quently light angle-bars are used for ties, but various 



CITY STREETS. 225 

other sections have also been employed for which 
special advantages are claimed. Spacing-rods between 
the webs of the rails may also be employed, as shown 
in Fig. 41, but these rods are objectionable in a block 




Fig. 41a. 

pavement on account of the difficulty of paving be- 
tween them. The ties are usually spaced about ten 
feet apart. 

In some instances, where concrete beams are used 
under the rails, ties are omitted altogether and the 
base of the rail is spiked directly to the concrete or 
bolted through the concrete beam to plates below. 
This latter method has been carried out at Rochester, 
N. Y., with entire success, no difficulty being experi- 
enced in holding the rails in position. In construct- 
ing such track the rails are usually laid on temporary 
wooden ties spaced ten or twelve feet apart and 
brought to line and grade, after which the concrete 
beams are placed and the wooden ties removed. 

Form for Rails. — The rails in common use for 
street-railway track are divided into two general 
classes: tee rails, as commonly used on steam roads, 
and girder rails, in which the head is so formed as to 
afford a channel for the flanges of the wheels and ad- 
mit of the p'iVement being laid close against the rail 
on both sides. 



2 26 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Tee rails differ considerably in their details and 
weights and are often modified for street service by 
making them of greater depth than is usual for steam- 
road service. These rails are shown in Figs. 38 and 
39. The upper surface varies from 2 to 3 inches in 
width and is usually made convex, the section being 
frequently circular, of radius 8 to 20 inches. As used 
for street railways, these rails vary from 4 to 7 inches 
in height. In using the smaller depths it is necessary, 
except for very thin paving surfaces, that the rails be 
supported on chairs or stringers to give room for paving 
over the cross-ties, and deeper sections are therefore 
more commonly used. The six-inch depth is fre- 
quently employed and is sufficient with an asphalt or 
brick pavement, the ties, if used, being embedded in 
the concrete foundation. 

The disadvantage of the tee rail consists in the fact 
that the pavement cannot come against the rail on the 
inside of the track, as it has no groove for the wheel- 
flange. The pavement must therefore either be low- 
ered under the rail-flange or a groove be left between 
the head of the rail and the pavement. The first 
method, shown in Fig. 38, is ordinarily the best con- 
struction, as the pavement is set firmly against the rails 
and there are no exposed edges to cause rapid wear, but 
it is objectionable on account of the impact of wheels 
crossing in dropping from the rail, and because it tends 
to hold the wheels of vehicles in the track. The 
second method is accomplished by using a thin block 
or a filling of concrete under the head of the rail and 
paving against this filling, as is usual when stone-block 
pavement is employed between the rails, or when a 
toothing of stone blocks or bricks is employed with 



CITY STREETS. 227 

an asphalt pavement. For brick pavements special 
bricks are sometimes molded to fit against the rails, 
leaving a groove for the wheel-flanges, as shown in 
Fig. 39. Difficulty has sometimes been met in the 
use of these bricks on account of their tendency to tilt 
when the car-wheel flanges press down any dirt or 
small gravel which may fall into the groove, unless 
they are very firmly bedded next the rail. Tee-rail 
construction is very commonly preferred by railway 
companies, as giving a better road for operation. It 
affords cheap construction, has little tendency to be- 
come clogged with dirt, and will usually be avoided 
by the ordinary traffic of the street, not affording good 
channels for the wheels of vehicles. 

Girder rails are divided as to form of head into 
center-bearing, side-bearing, and grooved. They 
vary, as commonly used, from 6 to 9 inches in height, 
and each type is subject to several variations in form. 

The centre-bearing rail is shown in Fig. 41^. It is 

the most objectionable of any of the 

forms in use, there being two channels, 

one on each side of the head, thus 

offering a double obstruction to traffic 

and causing greatly increased wear to 

the pavement. It is of advantage to 

the traffic of the railway because it 
, .1. 1 1 Fig. ^\b. 

does not retam dirt, and where streets 

are not kept in good condition cleanses itself, which 
is particularly important on electric roads in which 
the rail is used as a current-conductor. Its objection- 
able features, however, prevent its use in most places. 
Side-bearing rails are shown in Figs. 40, 41^, and 42. 
They are probably more commonly used than any 




228 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

other type of girder rail. The tram is from 2 to 3 
inches wide and offers a smooth track for the wheels 
of vehicles, but it is difficult for a wheel to leave it 
and is extremely hard on the street traffic. 

Pavements may be laid against the side-bearing rail 
as shown in Fig. 40, in which the surface of the pave- 
ment is at the same level inside as outside the track, 
or as shown in Fig. 41^, in which the pavement inside 




Fig. 41c, 

the track is brought even with the top of the tram of 
the rail. The first method leaves an exposed edge 
of the paving surface which is commonly subject to 
rapid wear, while the width of tram is sufficient to per- 
mit the wheels of vehicles to run in the grooves and to 
leave the track with difficulty. 

Grooved rails are shown in Figs. 37, 41, \\a, /\2ay 
and 42^. There are many variations in the form of 
groove and lip designed to meet varying conditions 
of use. The full-groove rail, shown in Fig. 37, has a 
groove in the head usually from an inch to an inch and 
a quarter in width, and when the pavement is made 
flush with the top of the rail it presents no obstruction 
to traffic of the street, and as the groove is too narrow 
to admit the wheels of vehicles it forms the most 
desirable track for use with smooth pavements. It 
can only, however, be used where pavements are kept 



CITY STREETS. 



229 



clean and in good condition, as the groove is otherwise 
easily clogged with dirt, rendering the operation of 
the railway difficult and expensive. This disadvantage 
is greater in cold climates where snow and ice are 
common during winter. 

For the purpose of lessening the clogging of the 
groove, the form of the grooved rail is sometimes 
modified by sloping the lip and widening the groove 
at the top, as shown in Fig. 41a, or, as shown in 





i-'^^^iT^™™^^ ^^^^^^m™ 




Fig. 42. 



Fig. 42a. 



Fig. 426. 



Fig. 42a, by making the lip of a less height than the 
head of the rail, thus allowing the wheel-flange to clear 
the groove of dirt in passing. This latter form, how- 
ever, has the effect of forming a track which retains 
the wheels of vehicles, as will any difference of ele- 
vation between the head of the rail and the pavement 
between the rails. 

In Fig. 42<^ is shown a grooved rail with an exten- 
sion of the lip intended to form a track for wheels of 
vehicles with a view to reducing the wear of the pave- 
ment which commonly takes place immediately inside 
the rails. When this lip is below the level of the 
rail-head it is subject to the same objection as the 



230 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

side-bearing rail of forming a track which it is difificult 
for wheels to leave. 

For paved streets, where the pavement is well kept, 
the grooved rail seems to be superior to any other, 
and is often required by municipal authorities, par- 
ticularly in the larger cities. For unimproved streets 
or on macadam or earth roads the tee rail is usually 
considered preferable, and may usually be employed 
with no more injury to the street traffic than any of 
the others, while possessing the advantage of economy 
both in cost and operation to the railway. 

Joints and Fastenings. — The solid construction of 
track is a matter of importance upon paved streets, 
because of the difficulty and expense of getting at the 
track to make repairs, as well as because of the dis- 
turbance to traffic when the pavement must be removed 
for this purpose. The rail-joints and tie-connections 
are therefore matters, requiring particular attention. 
Where no chairs are used, the use of tie-plates to form 
a bearing for the rail upon the tie, and to hold it 
securely in place, is to be recommended, and will 
greatly aid in forming a rigid track. There are a 
number of forms in use which give good results. 
They should be arranged to clamp the rail firmly and 
present a good bearing upon the tie. When chairs 
are used, they, like the tie-plates, should clamp the 
rail firmly and give good bearing surface. They 
should also be well braced for stiffness against lateral 
bending. 

Joints, in the case of track formed of rails laid di- 
rectly upon the ties, or upon wooden stringers, are 
usually made by placing a plate or channel-bar upon 
each side of the web of the rail-ends to be joined and 



CITY STREETS. 23 I 

bolting through. The use of slightly curved channel- 
bars fitting against the flanges of the rail, as shown 
in Figs. 42 and 42^, seems to give good results, the 
spring in the channels serving to prevent the loosening 
of the bolts. This is the most common method of 
making joints. Fig. /\.2a shows a pair of ribbed-joint 
plates as used for high rails, the centre bearing serving 
to prevent the buckling of the plates or the bending 
of the rail at the ends. 

For track in pavements the rails may be laid to 
close joints, no allowance being necessary for change 
of temperature when the rail is fully bedded in the 
pavement. 

A number of modifications of the above joints have 
been devised, some of them passing under the base of 
the rail and supporting it on the tie. Electrically 
welded or cast joints are also sometimes employed, 
consisting in welding a bar of steel on each side of the 
end of the rail, or in casting an iron block about the 
ends to be joined, the casting being joined by means 
of the holes through the web of the rails. 

Where chairs are employed to raise the rails above 
the ties, joints are frequently most satisfactorily made 
upon long chairs or bridges reaching across the space 
between two ties and forming a firm bearing for the 
ends of the rails. 

In order to facilitate keeping the joints tight and 
enable the bolts at the rail-ends to be screwed up 
without taking up the pavement, joint-boxes are 
sometimes employed. These consist of openings with 
removable covers, giving access to the bolts at the 
ends of the rails. 

On curves guard-rails are commonly employed. 



232 A TEXT-BOOK ON ROADS AND PAVEMENTS. 

Where tee rails are employed the guard is usually a 
second rail placed on the inside of the main rail, leav- 
ing only room for the wheel-flanges. In some instan- 
ces, however, the guard is formed by bolting a flange 
to the main rail. For girder rails the guard is usually 
formed by the use of a rail in which the groove is 
wider and the lip heavier than common, and sometimes 
the lip extends somewhat above the head of the rail. 
Any difference of elevation of that kind is objection- 
able as producing unevenness in the pavement, but is 
frequently used as essential to the proper operation of 
the cars upon the curves. 

Pavement in Car-tracks. — The wear of a pavement 
is usually considerably increased by railway tracks 
upon the street. The extent of this wear depends 
upon the nature of the paving surface as well as upon 
the construction of the track. It is mainly the differ- 
ence in resistance to abrasive wear between the rails 
and the paving surface which causes uneven and more 
rapid wear of the pavement in vicinity of the track. 
A broken-stone surface, on account of its rapid wear, 
is particularly objectionable along a line of track, and 
is very difficult to keep in proper surface. 

In the case of narrow streets or rough side-pave- 
ments the use of the track for hauling heavy loads 
causes the cutting of the pavement upon the outside 
of the track, due to the gauge of trucks being greater 
than that of the track. This is especially the case 
where, owing to the use of side-bearing or centre- 
bearing rails, the flange-grooves are wide enough to 
permit the wheels of trucks to enter them. 

Where tracks follow country roads it is usually 
desirable, if possible, to place the track at one side 



CITY STREETS. 233 

and leave the centre of the street free for the use of 
the ordinary traffic. When a broken-stone or gravel 
surface is employed it is common to lay planks on 
each side of the rail and bring the pavement against 
the planks, which materially lessens the obstruction 
offered to travel by the rails, as well as the difficulty 
of keeping the pavement in surface. 

The methods of placing pavements in tracks 
depend upon the shape of the rail-heads and have 
already been discussed. Under heavy traffic when 
asphalt street surface is employed it is quite common 
to pave between the rails with stone or brick, and 
often to put a toothing of the same material outside 
the rails adjoining the asphalt. This serves to prevent 
the cutting of the asphalt along the rails. Sometimes 
when stone blocks are used in track the concrete base 
is omitted and the blocks are set on a gravel or broken- 
stone base. When such construction is employed the 
track should be very carefully ballasted and brought 
to an even bearing. There is always a tendency for 
the track to work loose from the pavement and get 
out of surface, and under heavy traffic very firm con- 
struction is necessary to counteract this tendency. 

Art. 83. Trees for Streets. 

It is always desirable, wherever possible, to have 
streets, at least those devoted to residential purposes, 
lined with rows of trees upon each side, both for the 
purpose of giving shade and to add to the beauty of 
appearance of the street. 

The most satisfactory way of arranging trees is usually 
to have a tree space between the sidewalk and the curb 
in which the trees are planted in a straight line along 



S34 A. TEXT-BOOK ON ROADS AND PAVEMENTS. 

the Street. Sometimes in very wide streets a tree 
space or parking is arranged in the middle of the street, 
with a driveway on each side. Trees should be spaced 
in the rows at such distances as will permit each tree 
when fully grown to spread to its full natural dimen- 
sions, — which usually requires, for trees ordinarily em- 
ployed, from 25 to 40 feet. 

The selection of the variety of trees to be used for 
this purpose must of course depend upon climatic 
and local conditions. Those which rapidly attain their 
full size are usually to be preferred. They should 
have a graceful form and make a good shade, but the 
foliage should not be too dense. Evergreens are not 
generally desirable for this purpose. Where there is 
plenty of room for their development the large-grow- 
ing varieties with light foliage are handsome and desir- 
able. The size, however, must be suited to the space, 
and upon narrow streets, or where the trees are to be 
close to the buildings, they must be of small growth. 
The ease with which the tree may be grown and its 
liability to disease or to be affected by the contamina- 
tions of a city atmosphere must be considered, as the 
conditions under which street trees must be grown are 
not usually favorable to their best development. 

It is desirable, especially in cities of considerable 
size, that the planting and care of trees be under con- 
trol of the municipal authorities. Trees may then be" 
set with a view to the best general effect upon the 
street as a whole, the selection and planting of the 
trees may be properly done, and the trees after plant- 
ing may be systematically cared for. 



CITY STREETS. 



235 



Art. 84. Alleys. 

The pavements for alleys in cities are constructed in 
a manner similar to those for streets. Cobblestones, 
block-stone, brick, and asphalt are commonly employed. 

The maintenance of alleys in good condition is a 
matter of no less importance than the maintenance of 
streets, although it is more likely to be neglected. It 
is of special importance that the pavement of an alley 
be impervious, well drained, and easily cleaned. 

The surface drainage of alleys is secured either by 
forming the section as in a street, with a crown at the 
middle and gutters and curbs at the sides, or, as is com- 
monly preferable with narrow alleys, by placing the 
gutter at the middle and sloping the pavement from 
the sides to the centre. Where the gutter is in the 
middle it is common to make the bottom of the gutter 
of a flagstone 15 to 18 inches wide. Fig. 43 shows a 
centre-drained alley with block-stone pavement upon 
sand foundation. 

Where the pavement is cobble or rough blocks it is 



fe#?# 4iMi i ^M^^ H^^i»^ 



Fig. 43. 

desirable also to form side-gutters of flagstones in order 
to promote ready drainage. Such construction is rep- 




FlG. 44. 

resented in Fig. 44, which shows a cobble pavement 
on a gravel base, with curb and narrow sidewalk. 



t? 



36».5 8.ieoa. 



JAN 37 1902 



